David Goodger
The following are ideas, alternatives, and justifications that were considered for reStructuredText syntax, which did not originate with Setext or StructuredText. For an analysis of constructs which did originate with StructuredText or Setext, please see Problems With StructuredText. See the reStructuredText Markup Specification for full details of the established syntax.
The ideas are divided into sections:
Implemented: already done. The issues and alternatives are recorded here for posterity.
Not Implemented: these ideas won't be implemented.
Tabled: these ideas should be revisited in the future.
To Do: these ideas should be implemented. They're just waiting for a champion to resolve issues and get them done.
... Or Not To Do?: possible but questionable. These probably won't be implemented, but you never know.
Prior to the syntax for field lists being finalized, several alternatives were proposed.
Unadorned RFC 822 everywhere:
Author: Me Version: 1
Advantages: clean, precedent (RFC822-compliant). Disadvantage: ambiguous (these paragraphs are a prime example).
Conclusion: rejected.
Special case: use unadorned RFC 822 for the very first or very last text block of a document:
""" Author: Me Version: 1 The rest of the document... """
Advantages: clean, precedent (RFC822-compliant). Disadvantages: special case, flat (unnested) field lists only, still ambiguous:
""" Usage: cmdname [options] arg1 arg2 ... We obviously *don't* want the like above to be interpreted as a field list item. Or do we? """
Conclusion: rejected for the general case, accepted for specific contexts (PEPs, email).
Use a directive:
.. fields:: Author: Me Version: 1
Advantages: explicit and unambiguous, RFC822-compliant. Disadvantage: cumbersome.
Conclusion: rejected for the general case (but such a directive could certainly be written).
Use Javadoc-style:
@Author: Me @Version: 1 @param a: integer
Advantages: unambiguous, precedent, flexible. Disadvantages: non-intuitive, ugly, not RFC822-compliant.
Conclusion: rejected.
Use leading colons:
:Author: Me :Version: 1
Advantages: unambiguous, obvious (almost RFC822-compliant), flexible, perhaps even elegant. Disadvantages: no precedent, not quite RFC822-compliant.
Conclusion: accepted!
Use double colons:
Author:: Me Version:: 1
Advantages: unambiguous, obvious? (almost RFC822-compliant), flexible, similar to syntax already used for literal blocks and directives. Disadvantages: no precedent, not quite RFC822-compliant, similar to syntax already used for literal blocks and directives.
Conclusion: rejected because of the syntax similarity & conflicts.
Why is RFC822 compliance important? It's a universal Internet standard, and super obvious. Also, I'd like to support the PEP format (ulterior motive: get PEPs to use reStructuredText as their standard). But it would be easy to get used to an alternative (easy even to convert PEPs; probably harder to convert python-deviants ;-).
Unfortunately, without well-defined context (such as in email headers: RFC822 only applies before any blank lines), the RFC822 format is ambiguous. It is very common in ordinary text. To implement field lists unambiguously, we need explicit syntax.
The following question was posed in a footnote:
Should "bibliographic field lists" be defined at the parser level, or at the DPS transformation level? In other words, are they reStructuredText-specific, or would they also be applicable to another (many/every other?) syntax?
The answer is that bibliographic fields are a reStructuredText-specific markup convention. Other syntaxes may implement the bibliographic elements explicitly. For example, there would be no need for such a transformation for an XML-based markup syntax.
Interpreted Text "Roles"The original purpose of interpreted text was as a mechanism for descriptive markup, to describe the nature or role of a word or phrase. For example, in XML we could say "<function>len</function>" to mark up "len" as a function. It is envisaged that within Python docstrings (inline documentation in Python module source files, the primary market for reStructuredText) the role of a piece of interpreted text can be inferred implicitly from the context of the docstring within the program source. For other applications, however, the role may have to be indicated explicitly.
Interpreted text is enclosed in single backquotes (`).
Initially, it was proposed that an explicit role could be indicated as a word or phrase within the enclosing backquotes:
As a prefix, separated by a colon and whitespace:
`role: interpreted text`
As a suffix, separated by whitespace and a colon:
`interpreted text :role`
There are problems with the initial approach:
There could be ambiguity with interpreted text containing colons. For example, an index entry of "Mission: Impossible" would require a backslash-escaped colon.
The explicit role is descriptive markup, not content, and will not be visible in the processed output. Putting it inside the backquotes doesn't feel right; the role isn't being quoted.
Tony Ibbs suggested that the role be placed outside the backquotes:
role:`prefix` or `suffix`:role
This removes the embedded-colons ambiguity, but limits the role identifier to be a single word (whitespace would be illegal). Since roles are not meant to be visible after processing, the lack of whitespace support is not important.
The suggested syntax remains ambiguous with respect to ratios and some writing styles. For example, suppose there is a "signal" identifier, and we write:
...calculate the `signal`:noise ratio.
"noise" looks like a role.
As an improvement on #2, we can bracket the role with colons:
:role:`prefix` or `suffix`:role:
This syntax is similar to that of field lists, which is fine since both are doing similar things: describing.
This is the syntax chosen for reStructuredText.
Another alternative is two colons instead of one:
role::`prefix` or `suffix`::role
But this is used for analogies ("A:B::C:D": "A is to B as C is to D").
Both alternative #2 and #4 lack delimiters on both sides of the role, making it difficult to parse (by the reader).
Some kind of bracketing could be used:
Parentheses:
(role)`prefix` or `suffix`(role)
Braces:
{role}`prefix` or `suffix`{role}Square brackets:
[role]`prefix` or `suffix`[role]
Angle brackets:
<role>`prefix` or `suffix`<role>
(The overlap of *ML tags with angle brackets would be too confusing and precludes their use.)
Syntax #3 was chosen for reStructuredText.
term RoleAdd a "term" role for unfamiliar or specialized terminology? Probably not as a standard role; there is no real use case, and emphasis is enough for most cases. For semantic markup, authors may define a custom role or include the "html-roles.txt" standard definition file that defines (amongst others) the "dfn" role (the "html5" writer selects the corresponding HTML <dfn> element).
Anonymous HyperlinksAlan Jaffray came up with this idea, along with the following syntax:
Search the `Python DOC-SIG mailing list archives`{}_.
.. _: https://mail.python.org/pipermail/doc-sig/
The idea is sound and useful. I suggested a "double underscore" syntax:
Search the `Python DOC-SIG mailing list archives`__. .. __: https://mail.python.org/pipermail/doc-sig/
But perhaps single underscores are okay? The syntax looks better, but the hyperlink itself doesn't explicitly say "anonymous":
Search the `Python DOC-SIG mailing list archives`_. .. _: https://mail.python.org/pipermail/doc-sig/
Mixing anonymous and named hyperlinks becomes confusing. The order of targets is not significant for named hyperlinks, but it is for anonymous hyperlinks:
Hyperlinks: anonymous_, named_, and another anonymous_. .. _named: named .. _: anonymous1 .. _: anonymous2
Without the extra syntax of double underscores, determining which hyperlink references are anonymous may be difficult. We'd have to check which references don't have corresponding targets, and match those up with anonymous targets. Keeping to a simple consistent ordering (as with auto-numbered footnotes) seems simplest.
reStructuredText will use the explicit double-underscore syntax for anonymous hyperlinks. An alternative (see Reworking Explicit Markup (Round 1) below) for the somewhat awkward ".. __:" syntax is "__":
An anonymous__ reference. __ http://anonymousReworking Explicit Markup (Round 1)
Alan Jaffray came up with the idea of anonymous hyperlinks, added to reStructuredText. Subsequently it was asserted that hyperlinks (especially anonymous hyperlinks) would play an increasingly important role in reStructuredText documents, and therefore they require a simpler and more concise syntax. This prompted a review of the current and proposed explicit markup syntaxes with regards to improving usability.
Original syntax:
.. _blah: internal hyperlink target .. _blah: http://somewhere external hyperlink target .. _blah: blahblah_ indirect hyperlink target .. __: anonymous internal target .. __: http://somewhere anonymous external target .. __: blahblah_ anonymous indirect target .. [blah] http://somewhere footnote .. blah:: http://somewhere directive .. blah: http://somewhere comment
Note
The comment text was intentionally made to look like a hyperlink target.
Origins:
Except for the colon (a delimiter necessary to allow for phrase-links), hyperlink target .. _blah: comes from Setext.
Comment syntax from Setext.
Footnote syntax from StructuredText ("named links").
Directives and anonymous hyperlinks original to reStructuredText.
Advantages:
Consistent explicit markup indicator: "..".
Consistent hyperlink syntax: ".. _" & ":".
Disadvantages:
Anonymous target markup is awkward: ".. __:".
The explicit markup indicator ("..") is excessively overloaded?
Comment text is limited (can't look like a footnote, hyperlink, or directive). But this is probably not important.
Alan Jaffray's proposed syntax #1:
__ _blah internal hyperlink target __ blah: http://somewhere external hyperlink target __ blah: blahblah_ indirect hyperlink target __ anonymous internal target __ http://somewhere anonymous external target __ blahblah_ anonymous indirect target __ [blah] http://somewhere footnote .. blah:: http://somewhere directive .. blah: http://somewhere comment
The hyperlink-connoted underscores have become first-level syntax.
Advantages:
Anonymous targets are simpler.
All hyperlink targets are one character shorter.
Disadvantages:
Inconsistent internal hyperlink targets. Unlike all other named hyperlink targets, there's no colon. There's an extra leading underscore, but we can't drop it because without it, "blah" looks like a relative URI. Unless we restore the colon:
__ blah: internal hyperlink target
Obtrusive markup?
Alan Jaffray's proposed syntax #2:
.. _blah internal hyperlink target .. blah: http://somewhere external hyperlink target .. blah: blahblah_ indirect hyperlink target .. anonymous internal target .. http://somewhere anonymous external target .. blahblah_ anonymous indirect target .. [blah] http://somewhere footnote !! blah: http://somewhere directive ## blah: http://somewhere comment
Leading underscores have been (almost) replaced by "..", while comments and directives have gained their own syntax.
Advantages:
Anonymous hyperlinks are simpler.
Unique syntax for comments. Connotation of "comment" from some programming languages (including our favorite).
Unique syntax for directives. Connotation of "action!".
Disadvantages:
Inconsistent internal hyperlink targets. Again, unlike all other named hyperlink targets, there's no colon. There's a leading underscore, matching the trailing underscores of references, which no other hyperlink targets have. We can't drop that one leading underscore though: without it, "blah" looks like a relative URI. Again, unless we restore the colon:
.. blah: internal hyperlink target
All (except for internal) hyperlink targets lack their leading underscores, losing the "hyperlink" connotation.
Obtrusive syntax for comments. Alternatives:
;; blah: http://somewhere
(also comment syntax in Lisp & others)
,, blah: http://somewhere
("comma comma": sounds like "comment"!)Iffy syntax for directives. Alternatives?
Tony Ibbs' proposed syntax:
.. _blah: internal hyperlink target .. _blah: http://somewhere external hyperlink target .. _blah: blahblah_ indirect hyperlink target .. anonymous internal target .. http://somewhere anonymous external target .. blahblah_ anonymous indirect target .. [blah] http://somewhere footnote .. blah:: http://somewhere directive .. blah: http://somewhere comment
This is the same as the current syntax, except for anonymous targets which drop their "__: ".
Advantage:
Anonymous targets are simpler.
Disadvantages:
Anonymous targets lack their leading underscores, losing the "hyperlink" connotation.
Anonymous targets are almost indistinguishable from comments. (Better to know "up front".)
David Goodger's proposed syntax: Perhaps going back to one of Alan's earlier suggestions might be the best solution. How about simply adding "__ " as a synonym for ".. __: " in the original syntax? These would become equivalent:
.. __: anonymous internal target .. __: http://somewhere anonymous external target .. __: blahblah_ anonymous indirect target __ anonymous internal target __ http://somewhere anonymous external target __ blahblah_ anonymous indirect target
Alternative 5 has been adopted.
Backquotes in Phrase-Links[From a 2001-06-05 Doc-SIG post in reply to questions from Doug Hellmann.]
The first draft of the spec, posted to the Doc-SIG in November 2000, used square brackets for phrase-links. I changed my mind because:
In the first draft, I had already decided on single-backquotes for inline literal text.
However, I wanted to minimize the necessity for backslash escapes, for example when quoting Python repr-equivalent syntax that uses backquotes.
The processing of identifiers (function/method/attribute/module etc. names) into hyperlinks is a useful feature. PyDoc recognizes identifiers heuristically, but it doesn't take much imagination to come up with counter-examples where PyDoc's heuristics would result in embarrassing failure. I wanted to do it deterministically, and that called for syntax. I called this construct "interpreted text".
Leveraging off the *emphasis*/**strong** syntax, lead to the idea of using double-backquotes as syntax.
I worked out some rules for inline markup recognition.
In combination with #5, double backquotes lent themselves to inline literals, neatly satisfying #2, minimizing backslash escapes. In fact, the spec says that no interpretation of any kind is done within double-backquote inline literal text; backslashes do no escaping within literal text.
Single backquotes are then freed up for interpreted text.
I already had square brackets required for footnote references.
Since interpreted text will typically turn into hyperlinks, it was a natural fit to use backquotes as the phrase-quoting syntax for trailing-underscore hyperlinks.
The original inspiration for the trailing underscore hyperlink syntax was Setext. But for phrases Setext used a very cumbersome underscores_between_words_like_this_ syntax.
The underscores can be viewed as if they were right-pointing arrows: -->. So hyperlink_ points away from the reference, and .. _hyperlink: points toward the target.
Substitution MechanismSubstitutions arose out of a Doc-SIG thread begun on 2001-10-28 by Alan Jaffray, "reStructuredText inline markup". It reminded me of a missing piece of the reStructuredText puzzle, first referred to in my contribution to "Documentation markup & processing / PEPs" (Doc-SIG 2001-06-21).
Substitutions allow the power and flexibility of directives to be shared by inline text. They are a way to allow arbitrarily complex inline objects, while keeping the details out of the flow of text. They are the equivalent of SGML/XML's named entities. For example, an inline image (using reference syntax alternative 4d (vertical bars) and definition alternative 3, the alternatives chosen for inclusion in the spec):
The |biohazard| symbol must be used on containers used to dispose of medical waste. .. |biohazard| image:: biohazard.png [height=20 width=20]
The |biohazard| substitution reference will be replaced in-line by whatever the .. |biohazard| substitution definition generates (in this case, an image). A substitution definition contains the substitution text bracketed with vertical bars, followed by a an embedded inline-compatible directive, such as "image". A transform is required to complete the substitution.
Syntax alternatives for the reference:
Use the existing interpreted text syntax, with a predefined role such as "sub":
The `biohazard`:sub: symbol...
Advantages: existing syntax, explicit. Disadvantages: verbose, obtrusive.
Use a variant of the interpreted text syntax, with a new suffix akin to the underscore in phrase-link references:
(a) `name`@ (b) `name`# (c) `name`& (d) `name`/ (e) `name`< (f) `name`:: (g) `name`:
Due to incompatibility with other constructs and ordinary text usage, (f) and (g) are not possible.
Use interpreted text syntax with a fixed internal format:
(a) `:name:` (b) `name:` (c) `name::` (d) `::name::` (e) `%name%` (f) `#name#` (g) `/name/` (h) `&name&` (i) `|name|` (j) `[name]` (k) `<name>` (l) `&name;` (m) `'name'`
To avoid ML confusion (k) and (l) are definitely out. Square brackets (j) won't work in the target (the substitution definition would be indistinguishable from a footnote).
The `/name/` syntax (g) is reminiscent of "s/find/sub" substitution syntax in ed-like languages. However, it may have a misleading association with regexps, and looks like an absolute POSIX path. (i) is visually equivalent and lacking the connotations.
A disadvantage of all of these is that they limit interpreted text, albeit only slightly.
Use specialized syntax, something new:
(a) #name# (b) @name@ (c) /name/ (d) |name| (e) <<name>> (f) //name// (g) ||name|| (h) ^name^ (i) [[name]] (j) ~name~ (k) !name! (l) =name= (m) ?name? (n) >name<
"#" (a) and "@" (b) are obtrusive. "/" (c) without backquotes looks just like a POSIX path; it is likely for such usage to appear in text.
"|" (d) and "^" (h) are feasible.
Redefine the trailing underscore syntax. See definition syntax alternative 4, below.
Syntax alternatives for the definition:
Use the existing directive syntax, with a predefined directive such as "sub". It contains a further embedded directive resolving to an inline-compatible object:
.. sub:: biohazard
.. image:: biohazard.png
[height=20 width=20]
.. sub:: parrot
That bird wouldn't *voom* if you put 10,000,000 volts
through it!
The advantages and disadvantages are the same as in inline alternative 1.
Use syntax as in #1, but with an embedded directivecompressed:
.. sub:: biohazard image:: biohazard.png [height=20 width=20]
This is a bit better than alternative 1, but still too much.
Use a variant of directive syntax, incorporating the substitution text, obviating the need for a special "sub" directive name. If we assume reference alternative 4d (vertical bars), the matching definition would look like this:
.. |biohazard| image:: biohazard.png [height=20 width=20]
(Suggested by Alan Jaffray on Doc-SIG from 2001-11-06.)
Instead of adding new syntax, redefine the trailing underscore syntax to mean "substitution reference" instead of "hyperlink reference". Alan's example:
I had lunch with Jonathan_ today. We talked about Zope_. .. _Jonathan: lj [user=jhl] .. _Zope: https://www.zope.dev/
A problem with the proposed syntax is that URIs which look like simple reference names (alphanum plus ".", "-", "_") would be indistinguishable from substitution directive names. A more consistent syntax would be:
I had lunch with Jonathan_ today. We talked about Zope_. .. _Jonathan: lj:: user=jhl .. _Zope: https://www.zope.dev/
(:: after .. _Jonathan: lj.)
The "Zope" target is a simple external hyperlink, but the "Jonathan" target contains a directive. Alan proposed is that the reference text be replaced by whatever the referenced directive (the "directive target") produces. A directive reference becomes a hyperlink reference if the contents of the directive target resolve to a hyperlink. If the directive target resolves to an icon, the reference is replaced by an inline icon. If the directive target resolves to a hyperlink, the directive reference becomes a hyperlink reference.
This seems too indirect and complicated for easy comprehension.
The reference in the text will sometimes become a link, sometimes not. Sometimes the reference text will remain, sometimes not. We don't know at the reference:
This is a `hyperlink reference`_; its text will remain. This is an `inline icon`_; its text will disappear.
That's a problem.
The syntax that has been incorporated into the spec and parser is reference alternative 4d with definition alternative 3:
The |biohazard| symbol... .. |biohazard| image:: biohazard.png [height=20 width=20]
We can also combine substitution references with hyperlink references, by appending a "_" (named hyperlink reference) or "__" (anonymous hyperlink reference) suffix to the substitution reference. This allows us to click on an image-link:
The |biohazard|_ symbol... .. |biohazard| image:: biohazard.png [height=20 width=20] .. _biohazard: https://www.cdc.gov/
There have been several suggestions for the naming of these constructs, originally called "substitution references" and "substitutions".
Candidate names for the reference construct:
substitution reference
tagging reference
inline directive reference
directive reference
indirect inline directive reference
inline directive placeholder
inline directive insertion reference
directive insertion reference
insertion reference
directive macro reference
macro reference
substitution directive reference
Candidate names for the definition construct:
substitution
substitution directive
tag
tagged directive
directive target
inline directive
inline directive definition
referenced directive
indirect directive
indirect directive definition
directive definition
indirect inline directive
named directive definition
inline directive insertion definition
directive insertion definition
insertion definition
insertion directive
substitution definition
directive macro definition
macro definition
substitution directive definition
substitution definition
"Inline directive reference" (1c) seems to be an appropriate term at first, but the term "inline" is redundant in the case of the reference. Its counterpart "inline directive definition" (2g) is awkward, because the directive definition itself is not inline.
"Directive reference" (1d) and "directive definition" (2k) are too vague. "Directive definition" could be used to refer to any directive, not just those used for inline substitutions.
One meaning of the term "macro" (1k, 2s, 2t) is too programming-language-specific. Also, macros are typically simple text substitution mechanisms: the text is substituted first and evaluated later. reStructuredText substitution definitions are evaluated in place at parse time and substituted afterwards.
"Insertion" (1h, 1i, 2n-2q) is almost right, but it implies that something new is getting added rather than one construct being replaced by another.
Which brings us back to "substitution". The overall best names are "substitution reference" (1a) and "substitution definition" (2v). A long way to go to add one word!
Inline External TargetsCurrently reStructuredText has two hyperlink syntax variations:
Named hyperlinks:
This is a named reference_ of one word ("reference"). Here is
a `phrase reference`_. Phrase references may even cross `line
boundaries`_.
.. _reference: https://www.example.org/reference/
.. _phrase reference: https://www.example.org/phrase_reference/
.. _line boundaries: https://www.example.org/line_boundaries/
Advantages:
The plaintext is readable.
Each target may be reused multiple times (e.g., just write "reference_" again).
No synchronized ordering of references and targets is necessary.
Disadvantages:
The reference text must be repeated as target names; could lead to mistakes.
The target URLs may be located far from the references, and hard to find in the plaintext.
Anonymous hyperlinks (in current reStructuredText):
This is an anonymous reference__. Here is an anonymous `phrase reference`__. Phrase references may even cross `line boundaries`__. __ https://www.example.org/reference/ __ https://www.example.org/phrase_reference/ __ https://www.example.org/line_boundaries/
Advantages:
The plaintext is readable.
The reference text does not have to be repeated.
Disadvantages:
References and targets must be kept in sync.
Targets cannot be reused.
The target URLs may be located far from the references.
For comparison and historical background, StructuredText also has two syntaxes for hyperlinks:
First, "reference text":URL:
This is a "reference":https://www.example.org/reference/
of one word ("reference"). Here is a "phrase
reference":https://www.example.org/phrase_reference/.Second, "reference text", https://example.org/absolute_URL:
This is a "reference", https://www.example.org/reference/
of one word ("reference"). Here is a "phrase reference",
https://www.example.org/phrase_reference/.Both syntaxes share advantages and disadvantages:
Advantages:
The target is specified immediately adjacent to the reference.
Disadvantages:
Poor plaintext readability.
Targets cannot be reused.
Both syntaxes use double quotes, common in ordinary text.
In the first syntax, the URL and the last word are stuck together, exacerbating the line wrap problem.
The second syntax is too magical; text could easily be written that way by accident (although only absolute URLs are recognized here, perhaps because of the potential for ambiguity).
A new type of "inline external hyperlink" has been proposed.
On 2002-06-28, Simon Budig proposed a new syntax for reStructuredText hyperlinks:
This is a reference_(https://www.example.org/reference/) of one
word ("reference"). Here is a `phrase
reference`_(https://www.example.org/phrase_reference/). Are
these examples, (single-underscore), named? If so, `anonymous
references`__(https://www.example.org/anonymous/) using two
underscores would probably be preferable.
The syntax, advantages, and disadvantages are similar to those of StructuredText.
Advantages:
The target is specified immediately adjacent to the reference.
Disadvantages:
Poor plaintext readability.
Targets cannot be reused (unless named, but the semantics are unclear).
Problems:
The "`ref`_(URL)" syntax forces the last word of the reference text to be joined to the URL, making a potentially very long word that can't be wrapped (URLs can be very long). The reference and the URL should be separate. This is a symptom of the following point:
The syntax produces a single compound construct made up of two equally important parts, with syntax in the middle, between the reference and the target. This is unprecedented in reStructuredText.
The "inline hyperlink" text is not a named reference (there's no lookup by name), so it shouldn't look like one.
According to the IETF standards RFC 2396 and RFC 2732, parentheses are legal URI characters and curly braces are legal email characters, making their use prohibitively difficult.
The named/anonymous semantics are unclear.
After an analysis of the syntax of (1) above, we came up with the following compromise syntax:
This is an anonymous reference__
__<https://www.example.org/reference/> of one word
("reference"). Here is a `phrase reference`__
__<https://www.example.org/phrase_reference/>. `Named
references`_ _<https://www.example.org/anonymous/> use single
underscores.
The syntax builds on that of the existing "inline internal targets": an _`inline internal target`.
Advantages:
The target is specified immediately adjacent to the reference, improving maintainability:
References and targets are easily kept in sync.
The reference text does not have to be repeated.
The construct is executed in two parts: references identical to existing references, and targets that are new but not too big a stretch from current syntax.
There's overwhelming precedent for quoting URLs with angle brackets [1].
Disadvantages:
Poor plaintext readability.
Lots of "line noise".
Targets cannot be reused (unless named; see below).
To alleviate the readability issue slightly, we could allow the target to appear later, such as after the end of the sentence:
This is a named reference__ of one word ("reference").
__<https://www.example.org/reference/> Here is a `phrase
reference`__. __<https://www.example.org/phrase_reference/>
Problem: this could only work for one reference at a time (reference/target pairs must be proximate [refA trgA refB trgB], not interleaved [refA refB trgA trgB] or nested [refA refB trgB trgA]). This variation is too problematic; references and inline external targets will have to be kept immediately adjacent (see (3) below).
The "reference__ __<target>" syntax is actually for "anonymous inline external targets", emphasized by the double underscores. It follows that single trailing and leading underscores would lead to implicitly named inline external targets. This would allow the reuse of targets by name. So after "reference_ _<target>", another "reference_" would point to the same target.
If it is best for references and inline external targets to be immediately adjacent, then they might as well be integrated. Here's an alternative syntax embedding the target URL in the reference:
This is an anonymous `reference <https://www.example.org
/reference/>`__ of one word ("reference"). Here is a `phrase
reference <https://www.example.org/phrase_reference/>`__.
Advantages and disadvantages are similar to those in (2). Readability is still an issue, but the syntax is a bit less heavyweight (reduced line noise). Backquotes are required, even for one-word references; the target URL is included within the reference text, forcing a phrase context.
We'll call this variant "embedded URIs".
Problem: how to refer to a title like "HTML Anchors: <a>" (which ends with an HTML/SGML/XML tag)? We could either require more syntax on the target (like "`reference text __<https://example.org/>`__"), or require the odd conflicting title to be escaped (like "`HTML Anchors: \<a>`__"). The latter seems preferable, and not too onerous.
Similarly to (2) above, a single trailing underscore would convert the reference & inline external target from anonymous to implicitly named, allowing reuse of targets by name.
I think this is the least objectionable of the syntax alternatives.
Other syntax variations have been proposed (by Brett Cannon and Benja Fallenstein):
`phrase reference`->https://www.example.org `phrase reference`@https://www.example.org `phrase reference`__ ->https://www.example.org `phrase reference` [-> https://www.example.org] `phrase reference`__ [-> https://www.example.org] `phrase reference` <https://www.example.org>_
None of these variations are clearly superior to #3 above. Some have problems that exclude their use.
With any kind of inline external target syntax it comes down to the conflict between maintainability and plaintext readability. I don't see a major problem with reStructuredText's maintainability, and I don't want to sacrifice plaintext readability to "improve" it.
The proponents of inline external targets want them for easily maintainable web pages. The arguments go something like this:
Named hyperlinks are difficult to maintain because the reference text is duplicated as the target name.
To which I said, "So use anonymous hyperlinks."
Anonymous hyperlinks are difficult to maintain because the references and targets have to be kept in sync.
"So keep the targets close to the references, grouped after each paragraph. Maintenance is trivial."
But targets grouped after paragraphs break the flow of text.
"Surely less than URLs embedded in the text! And if the intent is to produce web pages, not readable plaintext, then who cares about the flow of text?"
Many participants have voiced their objections to the proposed syntax:
Garth Kidd: "I strongly prefer the current way of doing it. Inline is spectactularly messy, IMHO."
Tony Ibbs: "I vehemently agree... that the inline alternatives being suggested look messy - there are/were good reasons they've been taken out... I don't believe I would gain from the new syntaxes."
Paul Moore: "I agree as well. The proposed syntax is far too punctuation-heavy, and any of the alternatives discussed are ambiguous or too subtle."
Others have voiced their support:
fantasai: "I agree with Simon. In many cases, though certainly not in all, I find parenthesizing the url in plain text flows better than relegating it to a footnote."
Ken Manheimer: "I'd like to weigh in requesting some kind of easy, direct inline reference link."
(Interesting that those against the proposal have been using reStructuredText for a while, and those for the proposal are either new to the list ["fantasai", background unknown] or longtime StructuredText users [Ken Manheimer].)
I was initially ambivalent/against the proposed "inline external targets". I value reStructuredText's readability very highly, and although the proposed syntax offers convenience, I don't know if the convenience is worth the cost in ugliness. Does the proposed syntax compromise readability too much, or should the choice be left up to the author? Perhaps if the syntax is allowed but its use strongly discouraged, for aesthetic/readability reasons?
After a great deal of thought and much input from users, I've decided that there are reasonable use cases for this construct. The documentation should strongly caution against its use in most situations, recommending independent block-level targets instead. Syntax #3 above ("embedded URIs") will be used.
Doctree Representation of Transitions(Although not reStructuredText-specific, this section fits best in this document.)
Having added the "horizontal rule" construct to the reStructuredText Markup Specification, a decision had to be made as to how to reflect the construct in the implementation of the document tree. Given this source:
Document ======== Paragraph 1 -------- Paragraph 2
The horizontal rule indicates a "transition" (in prose terms) or the start of a new "division". Before implementation, the parsed document tree would be:
<document>
<section names="document">
<title>
Document
<paragraph>
Paragraph 1
-------- <--- error here
<paragraph>
Paragraph 2
There are several possibilities for the implementation:
Implement horizontal rules as "divisions" or segments. A "division" is a title-less, non-hierarchical section. The first try at an implementation looked like this:
<document>
<section names="document">
<title>
Document
<paragraph>
Paragraph 1
<division>
<paragraph>
Paragraph 2
But the two paragraphs are really at the same level; they shouldn't appear to be at different levels. There's really an invisible "first division". The horizontal rule splits the document body into two segments, which should be treated uniformly.
Treating "divisions" uniformly brings us to the second possibility:
<document>
<section names="document">
<title>
Document
<division>
<paragraph>
Paragraph 1
<division>
<paragraph>
Paragraph 2
With this change, documents and sections will directly contain divisions and sections, but not body elements. Only divisions will directly contain body elements. Even without a horizontal rule anywhere, the body elements of a document or section would be contained within a division element. This makes the document tree deeper. This is similar to the way HTML treats document contents: grouped within a <body> element.
Implement them as "transitions", empty elements:
<document>
<section names="document">
<title>
Document
<paragraph>
Paragraph 1
<transition>
<paragraph>
Paragraph 2
A transition would be a "point element", not containing anything, only identifying a point within the document structure. This keeps the document tree flatter, but the idea of a "point element" like "transition" smells bad. A transition isn't a thing itself, it's the space between two divisions. However, transitions are a practical solution.
Solution 3 was chosen for incorporation into the document tree model.
Syntax for Line BlocksAn early idea: How about a literal-block-like prefix, perhaps ";;"? (It is, after all, a semi-literal literal block, no?) Example:
Take it away, Eric the Orchestra Leader! ;;
A one, two, a one two three four
Half a bee, philosophically,
must, *ipso facto*, half not be.
But half the bee has got to be,
*vis a vis* its entity. D'you see?
But can a bee be said to be
or not to be an entire bee,
when half the bee is not a bee,
due to some ancient injury?
Singing...
Kinda lame.
Another idea: in an ordinary paragraph, if the first line ends with a backslash (escaping the newline), interpret the entire paragraph as a verse block? For example:
Add just one backslash\ And this paragraph becomes An awful haiku
(Awful, and arguably invalid, since in Japanese the word "haiku" contains three syllables not two.)
This idea was superseded by the rules for escaped whitespace, useful for character-level inline markup.
In a 2004-02-22 docutils-develop message, Jarno Elonen proposed a "plain list" syntax (and also provided a patch):
| John Doe | President, SuperDuper Corp. | jdoe@example.org
This syntax is very natural. However, these "plain lists" seem very similar to line blocks, and I see so little intrinsic "list-ness" that I'm loathe to add a new object. I used the term "blurbs" to remove the "list" connotation from the originally proposed name. Perhaps line blocks could be refined to add the two properties they currently lack:
long lines wrap nicely
HTML output doesn't look like program code in non-CSS web browsers
(A) is an issue of all 3 aspects of Docutils: syntax (construct behaviour), internal representation, and output. (B) is partly an issue of internal representation but mostly of output.
ReStructuredText will redefine line blocks with the "|"-quoting syntax. The following is my current thinking.
SyntaxPerhaps line block syntax like this would do:
| M6: James Bond | MIB: Mr. J. | IMF: not decided yet, but probably one of the following: | Ethan Hunt | Jim Phelps | Claire Phelps | CIA: Lea Leiter
Note that the "nested" list does not have nested syntax (the "|" are not further indented); the leading whitespace would still be significant somehow (more below). As for long lines in the input, this could suffice:
| John Doe | Founder, President, Chief Executive Officer, Cook, Bottle Washer, and All-Round Great Guy | SuperDuper Corp. | jdoe@example.org
The lack of "|" on the third line indicates that it's a continuation of the second line, wrapped.
I don't see much point in allowing arbitrary nested content. Multiple paragraphs or bullet lists inside a "blurb" doesn't make sense to me. Simple nested line blocks should suffice.
Internal RepresentationLine blocks are currently represented as text blobs as follows:
<!ELEMENT line_block %text.model;>
<!ATTLIST line_block
%basic.atts;
%fixedspace.att;>
Instead, we could represent each line by a separate element:
<!ELEMENT line_block (line+)> <!ATTLIST line_block %basic.atts;> <!ELEMENT line %text.model;> <!ATTLIST line %basic.atts;>
We'd keep the significance of the leading whitespace of each line either by converting it to non-breaking spaces at output, or with a per-line margin. Non-breaking spaces are simpler (for HTML, anyway) but kludgey, and wouldn't support indented long lines that wrap. But should inter-word whitespace (i.e., not leading whitespace) be preserved? Currently it is preserved in line blocks.
Representing a more complex line block may be tricky:
| But can a bee be said to be | or not to be an entire bee, | when half the bee is not a bee, | due to some ancient injury?
Perhaps the representation could allow for nested line blocks:
<!ELEMENT line_block (line | line_block)+>
With this model, leading whitespace would no longer be significant. Instead, left margins are implied by the nesting. The example above could be represented as follows:
<line_block>
<line>
But can a bee be said to be
<line_block>
<line>
or not to be an entire bee,
<line_block>
<line>
when half the bee is not a bee,
<line_block>
<line>
due to some ancient injury?
I wasn't sure what to do about even more complex line blocks:
| Indented | Not indented | Indented a bit | A bit more | Only one space
How should that be parsed and nested? Should the first line have the same nesting level (== indentation in the output) as the fourth line, or the same as the last line? Mark Nodine suggested that such line blocks be parsed similarly to complexly-nested block quotes, which seems reasonable. In the example above, this would result in the nesting of first line matching the last line's nesting. In other words, the nesting would be relative to neighboring lines only.
OutputIn HTML, line blocks are currently output as "<pre>" blocks, which gives us significant whitespace and line breaks, but doesn't allow long lines to wrap and causes monospaced output without stylesheets. Instead, we could output "<div>" elements parallelling the representation above, where each nested <div class="line_block"> would have an increased left margin (specified in the stylesheet).
Jarno suggested the following HTML output:
<div class="line_block">
<span class="line">First, top level line</span><br class="hidden"/>
<div class="line_block"><span class="hidden"> </span>
<span class="line">Second, once nested</span><br class="hidden"/>
<span class="line">Third, once nested</span><br class="hidden"/>
...
</div>
...
</div>
The <br class="hidden" /> and <span class="hidden"> </span> are meant to support non-CSS and non-graphical browsers. I understand the case for "br", but I'm not so sure about hidden " ". I question how much effort should be put toward supporting non-graphical and especially non-CSS browsers, at least for html4css1.py output.
Should the lines themselves be <span> or <div>? I don't like mixing inline and block-level elements.
Implementation PlanWe'll leave the old implementation in place (via the "line-block" directive only) until all Writers have been updated to support the new syntax & implementation. The "line-block" directive can then be updated to use the new internal representation, and its documentation will be updated to recommend the new syntax.
List-Driven TablesThe original idea came from Dylan Jay:
... to use a two level bulleted list with something to indicate it should be rendered as a table ...
It's an interesting idea. It could be implemented in as a directive which transforms a uniform two-level list into a table. Using a directive would allow the author to explicitly set the table's orientation (by column or by row), the presence of row headers, etc.
Alternatives:
(Implemented in Docutils 0.3.8).
Bullet-list-tables might look like this:
.. list-table::
* - Treat
- Quantity
- Description
* - Albatross!
- 299
- On a stick!
* - Crunchy Frog!
- 1499
- If we took the bones out, it wouldn't be crunchy,
now would it?
* - Gannet Ripple!
- 199
- On a stick!
This list must be written in two levels. This wouldn't work:
.. list-table:: * Treat * Albatross! * Gannet! * Crunchy Frog! * Quantity * 299 * 199 * 1499 * Description * On a stick! * On a stick! * If we took the bones out...
The above is a single list of 12 items. The blank lines are not significant to the markup. We'd have to explicitly specify how many columns or rows to use, which isn't a good idea.
Beni Cherniavsky suggested a field list alternative. It could look like this:
.. field-list-table::
:headrows: 1
- :treat: Treat
:quantity: Quantity
:descr: Description
- :treat: Albatross!
:quantity: 299
:descr: On a stick!
- :treat: Crunchy Frog!
:quantity: 1499
:descr: If we took the bones out, it wouldn't be
crunchy, now would it?
Column order is determined from the order of fields in the first row. Field order in all other rows is ignored. As a side-effect, this allows trivial re-arrangement of columns. By using named fields, it becomes possible to omit fields in some rows without losing track of things, which is important for spans.
An alternative to two-level bullet lists would be to use enumerated lists for the table cells:
.. list-table::
* 1. Treat
2. Quantity
3. Description
* 1. Albatross!
2. 299
3. On a stick!
* 1. Crunchy Frog!
2. 1499
3. If we took the bones out, it wouldn't be crunchy,
now would it?
That provides better correspondence between cells in the same column than does bullet-list syntax, but not as good as field list syntax. I think that were only field-list-tables available, a lot of users would use the equivalent degenerate case:
.. field-list-table::
- :1: Treat
:2: Quantity
:3: Description
...Another natural variant is to allow a description list with field lists as descriptions:
.. list-table::
:headrows: 1
Treat
:quantity: Quantity
:descr: Description
Albatross!
:quantity: 299
:descr: On a stick!
Crunchy Frog!
:quantity: 1499
:descr: If we took the bones out, it wouldn't be
crunchy, now would it?
This would make the whole first column a header column ("stub"). It's limited to a single column and a single paragraph fitting on one source line. Also it wouldn't allow for empty cells or row spans in the first column. But these are limitations that we could live with, like those of simple tables.
The List-driven table feature could be done in many ways. Each user will have their preferred usage. Perhaps a single "list-table" directive could handle them all, depending on which options and content are present.
Issues:
How to indicate that there's 1 header row? Perhaps two lists?
.. list-table::
+ - Treat
- Quantity
- Description
* - Albatross!
- 299
- On a stick!
This is probably too subtle though. Better would be a directive option, like :headrows: 1. An early suggestion for the header row(s) was to use a directive option:
.. field-list-table::
:header:
- :treat: Treat
:quantity: Quantity
:descr: Description
- :treat: Albatross!
:quantity: 299
:descr: On a stick!
But the table data is at two levels and looks inconsistent.
In general, we cannot extract the header row from field lists' field names because field names cannot contain everything one might put in a table cell. A separate header row also allows shorter field names and doesn't force one to rewrite the whole table when the header text changes. But for simpler cases, we can offer a ":header: fields" option, which does extract header cells from field names:
.. field-list-table::
:header: fields
- :Treat: Albatross!
:Quantity: 299
:Description: On a stick!How to indicate the column widths? A directive option?
.. list-table:: :widths: 15 10 35
Automatic defaults from the text used?
How to handle row and/or column spans?
In a field list, column-spans can be indicated by specifying the first and last fields, separated by space-dash-space or ellipsis:
- :foo - baz: quuux - :foo ... baz: quuux
Commas were proposed for column spans:
- :foo, bar: quux
But non-adjacent columns become problematic. Should we report an error, or duplicate the value into each span of adjacent columns (as was suggested)? The latter suggestion is appealing but may be too clever. Best perhaps to simply specify the two ends.
It was suggested that comma syntax should be allowed, too, in order to allow the user to avoid trouble when changing the column order. But changing the column order of a table with spans is not trivial; we shouldn't make it easier to mess up.
One possible syntax for row-spans is to simply treat any row where a field is missing as a row-span from the last row where it appeared. Leaving a field empty would still be possible by writing a field with empty content. But this is too implicit.
Another way would be to require an explicit continuation marker (.../-"-/"?) in all but the first row of a spanned field. Empty comments could work (".."). If implemented, the same marker could also be supported in simple tables, which lack row-spanning abilities.
Explicit markup like ":rowspan:" and ":colspan:" was also suggested.
Sometimes in a table, the first header row contains spans. It may be necessary to provide a way to specify the column field names independently of data rows. A directive option would do it.
We could specify "column-wise" or "row-wise" ordering, with the same markup structure. For example, with definition data:
.. list-table::
:column-wise:
Treat
- Albatross!
- Crunchy Frog!
Quantity
- 299
- 1499
Description
- On a stick!
- If we took the bones out, it wouldn't be
crunchy, now would it?A syntax for stubs in grid tables is easy to imagine:
+------------------------++------------+----------+ | Header row, column 1 || Header 2 | Header 3 | +========================++============+==========+ | body row 1, column 1 || column 2 | column 3 | +------------------------++------------+----------+
Or this idea from Nick Moffitt:
+-----+---+---+ | XOR # T | F | +=====+===+===+ | T # F | T | +-----+---+---+ | F # T | F | +-----+---+---+
Implemented 2005-03-24: combination of variation 1 & 2.
The advantage of auto-numbered enumerated lists would be similar to that of auto-numbered footnotes: lists could be written and rearranged without having to manually renumber them. The disadvantages are also the same: input and output wouldn't match exactly; the markup may be ugly or confusing (depending on which alternative is chosen).
Use the "#" symbol. Example:
#. Item 1. #. Item 2. #. Item 3.
Advantages: simple, explicit. Disadvantage: enumeration sequence cannot be specified (limited to arabic numerals); ugly.
As a variation on #1, first initialize the enumeration sequence? For example:
a) Item a. #) Item b. #) Item c.
Advantages: simple, explicit, any enumeration sequence possible. Disadvantages: ugly; perhaps confusing with mixed concrete/abstract enumerators.
Alternative suggested by Fred Bremmer, from experience with MoinMoin:
1. Item 1. 1. Item 2. 1. Item 3.
Advantages: enumeration sequence is explicit (could be multiple "a." or "(I)" tokens). Disadvantages: perhaps confusing; otherwise erroneous input (e.g., a duplicate item "1.") would pass silently, either causing a problem later in the list (if no blank lines between items) or creating two lists (with blanks).
Take this input for example:
1. Item 1. 1. Unintentional duplicate of item 1. 2. Item 2.
Currently the parser will produce two list, "1" and "1,2" (no warnings, because of the presence of blank lines). Using Fred's notation, the current behavior is "1,1,2 -> 1 1,2" (without blank lines between items, it would be "1,1,2 -> 1 [WARNING] 1,2"). What should the behavior be with auto-numbering?
Fred has produced a patch, whose initial behavior is as follows:
1,1,1 -> 1,2,3 1,2,2 -> 1,2,3 3,3,3 -> 3,4,5 1,2,2,3 -> 1,2,3 [WARNING] 3 1,1,2 -> 1,2 [WARNING] 2
(After the "[WARNING]", the "3" would begin a new list.)
I have mixed feelings about adding this functionality to the spec & parser. It would certainly be useful to some users (myself included; I often have to renumber lists). Perhaps it's too clever, asking the parser to guess too much. What if you do want three one-item lists in a row, each beginning with "1."? You'd have to use empty comments to force breaks. Also, I question whether "1,2,2 -> 1,2,3" is optimal behavior.
In response, Fred came up with "a stricter and more explicit rule [which] would be to only auto-number silently if all the enumerators of a list were identical". In that case:
1,1,1 -> 1,2,3 1,2,2 -> 1,2 [WARNING] 2 3,3,3 -> 3,4,5 1,2,2,3 -> 1,2 [WARNING] 2,3 1,1,2 -> 1,2 [WARNING] 2
Should any start-value be allowed ("3,3,3"), or should auto-numbered lists be limited to begin with ordinal-1 ("1", "A", "a", "I", or "i")?
Alternative proposed by Tony Ibbs:
#1. First item. #3. Aha - I edited this in later. #2. Second item.
The initial proposal required unique enumerators within a list, but this limits the convenience of a feature of already limited applicability and convenience. Not a useful requirement; dropped.
Instead, simply prepend a "#" to a standard list enumerator to indicate auto-enumeration. The numbers (or letters) of the enumerators themselves are not significant, except:
as a sequence indicator (arabic, roman, alphabetic; upper/lower),
and perhaps as a start value (first list item).
Advantages: explicit, any enumeration sequence possible. Disadvantages: a bit ugly.
A special case for inline markup was proposed and implemented: multiple citation references could be joined into one:
[cite1]_[cite2]_ instead of requiring [cite1]_ [cite2]_
However, this was rejected as an unwarranted exception to the rules for inline markup. (The main motivation for the proposal, grouping citations in the latex writer, was implemented by recognising the second group in the example above and transforming it into \cite{cite1,cite2}.)
Inline markup recognitionImplemented 2011-12-05 (version 0.9): Extended inline markup recognition rules.
Non-ASCII whitespace, punctuation characters and "international" quotes are allowed around inline markup (based on Unicode categories). The rules for ASCII characters were not changed.
Rejected alternatives:
Use Unicode categories for all chars (ASCII or not)
comprehensible, standards based,
many "false positives" need escaping,
not backwards compatible.
full backwards compatibility
only before start-string
only behind end-string
"conservative" sorting of other punctuation:
Close
Open
backwards compatible,
logical extension of the existing rules,
exception list for "other" punctuation needed,
rules even more complicated,
not clear how to sort "other" punctuation that is currently not recognized,
international quoting convention like »German âºangularâ¹ quotes« not recognized.
Implement as a generic two-column marked list? As a standalone (non-directive) construct? (Is the markup ambiguous?) Add support to parts.contents?
New elements would be required. Perhaps:
<!ELEMENT question_list (question_list_item+)>
<!ATTLIST question_list
numbering (none | local | global)
#IMPLIED
start NUMBER #IMPLIED>
<!ELEMENT question_list_item (question, answer*)>
<!ELEMENT question %text.model;>
<!ELEMENT answer (%body.elements;)+>
Originally I thought of implementing a Q&A list with special syntax:
Q: What am I? A: You are a question-and-answer list. Q: What are you? A: I am the omniscient "we".
Where each "Q" and "A" could also be numbered (e.g., "Q1"). However, a simple enumerated or bulleted list will do just fine for syntax. A directive could treat the list specially; e.g. the first paragraph could be treated as a question, the remainder as the answer (multiple answers could be represented by nested lists). Without special syntax, this directive becomes low priority.
As described in the FAQ, no special syntax or directive is needed for this application.
Tabled Reworking Explicit Markup (Round 2)See Reworking Explicit Markup (Round 1) for an earlier discussion.
In April 2004, a new thread becan on docutils-develop: Inconsistency in RST markup. Several arguments were made; the first argument begat later arguments. Below, the arguments are paraphrased "in quotes", with responses.
References and targets take this form:
targetname_ .. _targetname: stuff
But footnotes, "which generate links just like targets do", are written as:
[1]_ .. [1] stuff
"Footnotes should be written as":
[1]_ .. _[1]: stuff
But they're not the same type of animal. That's not a "footnote target", it's a footnote. Being a target is not a footnote's primary purpose (an arguable point). It just happens to grow a target automatically, for convenience. Just as a section title:
Title =====
isn't a "title target", it's a title, which happens to grow a target automatically. The consistency is there, it's just deeper than at first glance.
Also, ".. [1]" was chosen for footnote syntax because it closely resembles one form of actual footnote rendering. ".. _[1]:" is too verbose; excessive punctuation is required to get the job done.
For more of the reasoning behind the syntax, see Problems With StructuredText (Hyperlinks) and Reworking Footnotes.
"I expect directives to also look like .. this: [one colon] because that also closely parallels the link and footnote target markup."
There are good reasons for the two-colon syntax:
Two colons are used after the directive type for these reasons:
Two colons are distinctive, and unlikely to be used in common text.
Two colons avoids clashes with common comment text like:
.. Danger: modify at your own risk!If an implementation of reStructuredText does not recognize a directive (i.e., the directive-handler is not installed), a level-3 (error) system message is generated, and the entire directive block (including the directive itself) will be included as a literal block. Thus "::" is a natural choice.
The last reason is not particularly compelling; it's more of a convenient coincidence or mnemonic.
"Comments always seemed too easy. I almost never write comments. I'd have no problem writing '.. comment:' in front of my comments. In fact, it would probably be more readable, as comments should be set off strongly, because they are very different from normal text."
Many people do use comments though, and some applications of reStructuredText require it. For example, all reStructuredText PEPs (and this document!) have an Emacs stanza at the bottom, in a comment. Having to write ".. comment::" would be very obtrusive.
Comments should be dirt-easy to do. It should be easy to "comment out" a block of text. Comments in programming languages and other markup languages are invariably easy.
Any author is welcome to preface their comments with "Comment:" or "Do Not Print" or "Note to Editor" or anything they like. A "comment" directive could easily be implemented. It might be confused with admonition directives, like "note" and "caution" though. In unrelated (and unpublished and unfinished) work, adding a "comment" directive as a true document element was considered:
If structure is necessary, we could use a "comment" directive (to avoid nonsensical DTD changes, the "comment" directive could produce an untitled topic element).
"One of the goals of reStructuredText is to be readable by people who don't know it. This construction violates that: it is not at all obvious to the uninitiated that text marked by '..' is a comment. On the other hand, '.. comment:' would be totally transparent."
Totally transparent, perhaps, but also very obtrusive. Another of reStructuredText's goals is to be unobtrusive, and ".. comment::" would violate that. The goals of reStructuredText are many, and they conflict. Determining the right set of goals and finding solutions that best fit is done on a case-by-case basis.
Even readability is has two aspects. Being readable without any prior knowledge is one. Being as easily read in raw form as in processed form is the other. ".." may not contribute to the former aspect, but ".. comment::" would certainly detract from the latter.
"Recently I sent someone an rst document, and they got confused; I had to explain to them that '..' marks comments, unless it's a directive, etc..."
The explanation of directives is roundabout, defining comments in terms of not being other things. That's definitely a wart.
"Under the current system, a mistyped directive (with ':' instead of '::') will be silently ignored. This is an error that could easily go unnoticed."
A parser option/setting like "--comments-on-stderr" would help.
"I'd prefer to see double-dot-space / command / double-colon as the standard Docutils markup-marker. It's unusual enough to avoid being accidentally used. Everything that starts with a double-dot should end with a double-colon."
That would increase the punctuation verbosity of some constructs considerably.
Edward Loper proposed the following plan for backwards compatibility:
".. foo" will generate a deprecation warning to stderr, and nothing in the output (no system messages).
".. foo: bar" will be treated as a directive foo. If there is no foo directive, then do the normal error output.
".. foo:: bar" will generate a deprecation warning to stderr, and be treated as a directive. Or leave it valid?
So some existing documents might start printing deprecation warnings, but the only existing documents that would break would be ones that say something like:
.. warning: this should be a commentinstead of:
.. warning:: this should be a commentHere, we're trading fairly common a silent error (directive falsely treated as a comment) for a fairly uncommon explicitly flagged error (comment falsely treated as directive). To make things even easier, we could add a sentence to the unknown-directive error. Something like "If you intended to create a comment, please use '.. comment:' instead".
On one hand, I understand and sympathize with the points raised. On the other hand, I think the current syntax strikes the right balance (but I acknowledge a possible lack of objectivity). On the gripping hand, the comment and directive syntax has become well established, so even if it's a wart, it may be a wart we have to live with.
Making any of these changes would cause a lot of breakage or at least deprecation warnings. I'm not sure the benefit is worth the cost.
For now, we'll treat this as an unresolved legacy issue.
To Do Nested Inline MarkupThese are collected notes on a long-discussed issue. The original mailing list messages should be referred to for details.
In a 2001-10-31 discussion I wrote:
Try, for example, Ed Loper's 2001-03-21 post, which details some rules for nested inline markup. I think the complexity is prohibitive for the marginal benefit. (And if you can understand that tree without going mad, you're a better man than I. ;-)
Inline markup is already fragile. Allowing nested inline markup would only be asking for trouble IMHO. If it proves absolutely necessary, it can be added later. The rules for what can appear inside what must be well thought out first though.
âhttps://mail.python.org/pipermail/doc-sig/2001-October/002354.html
In a 2001-11-09 Doc-SIG post, I wrote:
The problem is that in the what-you-see-is-more-or-less-what-you-get markup language that is reStructuredText, the symbols used for inline markup ("*", "**", "`", "``", etc.) may preclude nesting.
I've rethought this position. Nested markup is not precluded, just tricky. People and software parse "double and 'single' quotes" all the time. Continuing,
I've thought over how we might implement nested inline markup. The first algorithm ("first identify the outer inline markup as we do now, then recursively scan for nested inline markup") won't work; counterexamples were given in my last post.
The second algorithm makes my head hurt:
while 1: scan for start-string if found: push on stack scan for start or end string if new start string found: recurse elif matching end string found: pop stack elif non-matching end string found: if its a markup error: generate warning elif the initial start-string was misinterpreted: # e.g. in this case: ***strong** in emphasis* restart with the other interpretation # but it might be several layers back ... ...This is similar to how the parser does section title recognition, but sections are much more regular and deterministic.
Bottom line is, I don't think the benefits are worth the effort, even if it is possible. I'm not going to try to write the code, at least not now. If somebody codes up a consistent, working, general solution, I'll be happy to consider it.
âhttps://mail.python.org/pipermail/doc-sig/2001-November/002388.html
In a 2003-05-06 Docutils-Users post Paul Tremblay proposed a new syntax to allow for easier nesting. It eventually evolved into this:
:role:[inline text]
The duplication with the existing interpreted text syntax is problematic though.
Could the parser be extended to parse nested interpreted text?
:emphasis:`Some emphasized text with :strong:`some more emphasized text` in it and **perhaps** :reference:`a link``
In a 2003-06-18 Docutils-Develop post, Mark Nodine reported on his implementation of a form of nested inline markup in his Perl-based parser (unpublished). He brought up some interesting ideas. The implementation was flawed, however, by the change in semantics required for backslash escapes.
Docutils-develop threads between David Abrahams, David Goodger, and Mark Nodine (beginning 2004-01-16 and 2004-01-19) hashed out many of the details of a potentially successful implementation, as described below. David Abrahams checked in code to the "nesting" branch of CVS, awaiting thorough review.
It may be possible to accomplish nested inline markup in general with a more powerful inline markup parser. There may be some issues, but I'm not averse to the idea of nested inline markup in general. I just don't have the time or inclination to write a new parser now. Of course, a good patch would be welcome!
I envisage something like this. Explicit-role interpreted text must be nestable. Prefix-based is probably preferred, since suffix-based will look like inline literals:
``text`:role1:`:role2:
But it can be disambiguated, so it ought to be left up to the author:
`\ `text`:role1:`:role2:
In addition, other forms of inline markup may be nested if unambiguous:
*emphasized ``literal`` and |substitution ref| and link_*
IOW, the parser ought to be as permissive as possible.
Index Entries & IndexesWere I writing a book with an index, I guess I'd need two different kinds of index targets: inline/implicit and out-of-line/explicit. For example:
In this `paragraph`:index:, several words are being
`marked`:index: inline as implicit `index`:index:
entries.
.. index:: markup
.. index:: syntax
The explicit index directives above would refer to
this paragraph. It might also make sense to allow multiple
entries in an ``index`` directive:
.. index::
markup
syntax
The words "paragraph", "marked", and "index" would become index entries pointing at the words in the first paragraph. The index entry words appear verbatim in the text. (Don't worry about the ugly ":index:" part; if indexing is the only/main application of interpreted text in your documents, it can be implicit and omitted.) The two directives provide manual indexing, where the index entry words ("markup" and "syntax") do not appear in the main text. We could combine the two directives into one:
.. index:: markup; syntax
Semicolons instead of commas because commas could be part of the index target, like:
.. index:: van Rossum, Guido
Another reason for index directives is because other inline markup wouldn't be possible within inline index targets.
Sometimes index entries have multiple levels. Given:
.. index:: statement syntax: expression statements
In a hypothetical index, combined with other entries, it might look like this:
statement syntax
expression statements ..... 56
assignment ................ 57
simple statements ......... 58
compound statements ....... 60
Inline multi-level index targets could be done too. Perhaps something like:
When dealing with `expression statements <statement syntax:>`, we must remember ...
The opposite sense could also be possible:
When dealing with `index entries <:multi-level>`, there are many permutations to consider.
Also "see / see also" index entries.
Given:
Here's a paragraph. .. index:: paragraph
(The "index" directive above actually targets the preceding object.) The directive should produce something like this XML:
<paragraph> <index_entry text="paragraph"/> Here's a paragraph. </paragraph>
This kind of content model would also allow true inline index-entries:
Here's a `paragraph`:index:.
If the "index" role were the default for the application, it could be dropped:
Here's a `paragraph`.
Both of these would result in this XML:
<paragraph> Here's a <index_entry>paragraph</index_entry>. </paragraph>from 2002-06-24 docutils-develop posts
If all of your index entries will appear verbatim in the text, this should be sufficient. If not (e.g., if you want "Van Rossum, Guido" in the index but "Guido van Rossum" in the text), we'll have to figure out a supplemental mechanism, perhaps using substitutions.
I've thought a bit more on this, and I came up with two possibilities:
Using interpreted text, embed the index entry text within the interpreted text:
... by `Guido van Rossum [Van Rossum, Guido]` ...
The problem with this is obvious: the text becomes cluttered and hard to read. The processed output would drop the text in brackets, which goes against the spirit of interpreted text.
Use substitutions:
... by |Guido van Rossum| ... .. |Guido van Rossum| index:: Van Rossum, Guido
A problem with this is that each substitution definition must have a unique name. A subsequent .. |Guido van Rossum| index:: BDFL would be illegal. Some kind of anonymous substitution definition mechanism would be required, but I think that's going too far.
Both of these alternatives are flawed. Any other ideas?
... Or Not To Do?This is the realm of the possible but questionably probable. These ideas are kept here as a record of what has been proposed, for posterity and in case any of them prove to be useful.
Compound Enumerated ListsAllow for compound enumerators, such as "1.1." or "1.a." or "1(a)", to allow for nested enumerated lists without indentation?
Indented ListsAllow for variant styles by interpreting indented lists as if they weren't indented? For example, currently the list below will be parsed as a list within a block quote:
paragraph * list item 1 * list item 2
But a lot of people seem to write that way, and HTML browsers make it look as if that's the way it should be. The parser could check the contents of block quotes, and if they contain only a single list, remove the block quote wrapper. There would be two problems:
What if we actually do want a list inside a block quote?
What if such a list comes immediately after an indented construct, such as a literal block?
Both could be solved using empty comments (problem 2 already exists for a block quote after a literal block). But that's a hack.
Perhaps a runtime setting, allowing or disabling this convenience, would be appropriate. But that raises issues too:
User A, who writes lists indented (and their config file is set up to allow it), sends a file to user B, who doesn't (and their config file disables indented lists). The result of processing by the two users will be different.
It may seem minor, but it adds ambiguity to the parser, which is bad.
See the Doc-SIG discussion starting 2001-04-18 with Ed Loper's "Structuring: a summary; and an attempt at EBNF", item 4 (and follow-ups, here and here). Also docutils-users, 2003-02-17 and beginning 2003-08-04.
Sloppy Indentation of List ItemsPerhaps the indentation shouldn't be so strict. Currently, this is required:
1. First line, second line.
Anything wrong with this?
1. First line, second line.
Problem?
1. First para.
Block quote. (no good: requires some indent relative to first
para)
Second Para.
2. Have to carefully define where the literal block ends::
Literal block
Literal block?
Hmm... Non-strict indentation isn't such a good idea. Except for field lists.
Lazy Indentation of List ItemsAnother approach: Going back to the first draft of reStructuredText (2000-11-27 post to Doc-SIG):
- This is the fourth item of the main list (no blank line above). The second line of this item is not indented relative to the bullet, which precludes it from having a second paragraph.
Change that to require a blank line above and below, to reduce ambiguity. This "loosening" may be added later, once the parser's been nailed down. However, a serious drawback of this approach is to limit the content of each list item to a single paragraph.
David's Idea for Lazy IndentationConsider a paragraph in a word processor. It is a single logical line of text which ends with a newline, soft-wrapped arbitrarily at the right edge of the page or screen. We can think of a plaintext paragraph in the same way, as a single logical line of text, ending with two newlines (a blank line) instead of one, and which may contain arbitrary line breaks (newlines) where it was accidentally hard-wrapped by an application. We can compensate for the accidental hard-wrapping by "unwrapping" every unindented second and subsequent line. The indentation of the first line of a paragraph or list item would determine the indentation for the entire element. Blank lines would be required between list items when using lazy indentation.
The following example shows the lazy indentation of multiple body elements:
- This is the first paragraph of the first list item. Here is the second paragraph of the first list item. - This is the first paragraph of the second list item. Here is the second paragraph of the second list item.
A more complex example shows the limitations of lazy indentation:
- This is the first paragraph
of the first list item.
Next is a definition list item:
Term
Definition. The indentation of the term is
required, as is the indentation of the definition's
first line.
When the definition extends to more than
one line, lazy indentation may occur. (This is the second
paragraph of the definition.)
- This is the first paragraph
of the second list item.
- Here is the first paragraph of
the first item of a nested list.
So this paragraph would be outside of the nested list,
but inside the second list item of the outer list.
But this paragraph is not part of the list at all.
And the ambiguity remains:
- Look at the hyphen at the beginning of the next line - is it a second list item marker, or a dash in the text? Similarly, we may want to refer to numbers inside enumerated lists: 1. How many socks in a pair? There are 2. How many pants in a pair? Exactly 1. Go figure.
Literal blocks and block quotes would still require consistent indentation for all their lines. For block quotes, we might be able to get away with only requiring that the first line of each contained element be indented. For example:
Here's a paragraph.
This is a paragraph inside a block quote.
Second and subsequent lines need not be indented at all.
- A bullet list inside
the block quote.
Second paragraph of the
bullet list inside the block quote.
Although feasible, this form of lazy indentation has problems. The document structure and hierarchy is not obvious from the indentation, making the source plaintext difficult to read. This will also make keeping track of the indentation while writing difficult and error-prone. However, these problems may be acceptable for Wikis and email mode, where we may be able to rely on less complex structure (few nested lists, for example).
Multiple Roles in Interpreted TextIn reStructuredText, inline markup cannot be nested (yet; see above). This also applies to interpreted text. In order to simultaneously combine multiple roles for a single piece of text, a syntax extension would be necessary. Ideas:
Initial idea:
`interpreted text`:role1,role2:
Suggested by Jason Diamond:
`interpreted text`:role1:role2:
If a document is so complex as to require nested inline markup, perhaps another markup system should be considered. By design, reStructuredText does not have the flexibility of XML.
Parameterized Interpreted TextIn some cases it may be expedient to pass parameters to interpreted text, analogous to function calls. Ideas:
Parameterize the interpreted text role itself (suggested by Jason Diamond):
`interpreted text`:role1(foo=bar):
Positional parameters could also be supported:
`CSS`:acronym(Cascading Style Sheets): is used for HTML, and `CSS`:acronym(Content Scrambling System): is used for DVDs.
Technical problem: current interpreted text syntax does not recognize roles containing whitespace. Design problem: this smells like programming language syntax, but reStructuredText is not a programming language.
Put the parameters inside the interpreted text:
`CSS (Cascading Style Sheets)`:acronym: is used for HTML, and `CSS (Content Scrambling System)`:acronym: is used for DVDs.
Although this could be defined on an individual basis (per role), we ought to have a standard. Hyperlinks with embedded URIs already use angle brackets; perhaps they could be used here too:
`CSS <Cascading Style Sheets>`:acronym: is used for HTML, and `CSS <Content Scrambling System>`:acronym: is used for DVDs.
Do angle brackets connote URLs too much for this to be acceptable? How about the "tag" connotation -- does it save them or doom them?
Nested inline markup could prove useful here:
`CSS :def:`Cascading Style Sheets``:acronym: is used for HTML, and `CSS :def:`Content Scrambling System``:acronym: is used for DVDs.
Inline markup roles could even define the default roles of nested inline markup, allowing this cleaner syntax:
`CSS `Cascading Style Sheets``:acronym: is used for HTML, and `CSS `Content Scrambling System``:acronym: is used for DVDs.
Does this push inline markup too far? Readability becomes a serious issue. Substitutions may provide a better alternative (at the expense of verbosity and duplication) by pulling the details out of the text flow:
|CSS| is used for HTML, and |CSS-DVD| is used for DVDs. .. |CSS| acronym:: Cascading Style Sheets .. |CSS-DVD| acronym:: Content Scrambling System :text: CSS
This whole idea may be going beyond the scope of reStructuredText. Documents requiring this functionality may be better off using XML or another markup system.
This argument comes up regularly when pushing the envelope of reStructuredText syntax. I think it's a useful argument in that it provides a check on creeping featurism. In many cases, the resulting verbosity produces such unreadable plaintext that there's a natural desire not to use it unless absolutely necessary. It's a matter of finding the right balance.
Syntax for Interpreted Text Role BindingsThe following syntax (idea from Jeffrey C. Jacobs) could be used to associate directives with roles:
.. :rewrite: class:: rewrite `She wore ribbons in her hair and it lay with streaks of grey`:rewrite:
The syntax is similar to that of substitution declarations, and the directive/role association may resolve implementation issues. The semantics, ramifications, and implementation details would need to be worked out.
The example above would implement the "rewrite" role as adding a class="rewrite" attribute to the interpreted text ("inline" element). The stylesheet would then pick up on the "class" attribute to do the actual formatting.
The advantage of the new syntax would be flexibility. Uses other than "class" may present themselves. The disadvantage is complexity: having to implement new syntax for a relatively specialized operation, and having new semantics in existing directives ("class::" would do something different).
The "role" directive has been implemented.
Character ProcessingSeveral people have suggested adding some form of character processing to reStructuredText:
Some sort of automated replacement of ASCII sequences:
-- to em-dash (or -- to en-dash, and --- to em-dash).
Convert quotes to curly quote entities. (Essentially impossible for HTML? Unnecessary for TeX.)
Various forms of :-) to smiley icons.
"\ " to . Problem with line-wrapping though: it could end up escaping the newline.
Escaped newlines to <BR>.
Escaped period or quote or dash as a disappearing catalyst to allow character-level inline markup?
XML-style character entities, such as "©" for the copyright symbol.
Docutils has no need of a character entity subsystem. Supporting Unicode and text encodings, character entities should be directly represented in the text: a copyright symbol should be represented by the copyright symbol character. If this is not possible in an authoring environment, a pre-processing stage can be added, or a table of substitution definitions can be devised.
A "unicode" directive has been implemented to allow direct specification of esoteric characters. In combination with the substitution construct, standard definition files for common sets of character entities are provided for inclusion.
To allow for character-level inline markup, a limited form of character processing has been added to the spec and parser: escaped whitespace characters are removed from the processed document. Any further character processing will be of this functional type, rather than of the character-encoding type.
Directive idea:
.. text-replace:: "pattern" "replacement"
Support Unicode "U+XXXX" codes.
Support regexps, perhaps with alternative "regexp-replace" directive.
Flags for regexps; ":flags:" option, or individuals.
Specifically, should the default be case-sensistive or -insensitive?
Should ^L (or something else in reST) be defined to mean force/suggest page breaks in whatever output we have?
A "break" or "page-break" directive would be easy to add. A new doctree element would be required though (perhaps "break"). The final behavior would be up to the Writer. The directive argument could be one of page/column/recto/verso for added flexibility.
Currently ^L (Python's \f) characters are treated as whitespace. They're converted to single spaces, actually, as are vertical tabs (^K, Python's \v). It would be possible to recognize form feeds as markup, but it requires some thought and discussion first. Are there any downsides? Many editing environments do not allow the insertion of control characters. Will it cause any harm? It would be useful as a shorthand for the directive.
It's common practice to use ^L before Emacs "Local Variables" lists (to prevent misinterpretation of unrelated text):
^L .. Local Variables: mode: indented-text indent-tabs-mode: nil sentence-end-double-space: t fill-column: 70 End:
These are already present in many PEPs and Docutils project documents. From the Emacs manual (info):
A "local variables list" goes near the end of the file, in the last page. (It is often best to put it on a page by itself.)
It would be unfortunate if this construct caused a final blank page to be generated (for those Writers that recognize the page breaks). We'll have to add a transform that looks for a "break" plus zero or more comments at the end of a document, and removes them.
Probably a bad idea because there is no such thing as a page in a generic document format.
Could the "break" concept above be extended to inline forms? E.g. "^L" in the middle of a sentence could cause a line break. Only recognize it at the end of a line (i.e., \f\n)?
Or is formfeed inappropriate? Perhaps vertical tab (\v), but even that's a stretch. Can't use carriage returns, since they're commonly used for line endings.
Probably a bad idea as well because we do not want to use control characters for well-readable and well-writable markup, and after all we have the line block syntax for line breaks.
Add ^superscript^ inline markup? The only common non-markup uses of "^" I can think of are as short hand for "superscript" itself and for describing control characters ("^C to cancel"). The former supports the proposed syntax, and it could be argued that the latter ought to be literal text anyhow (e.g. "^C to cancel").
However, superscripts are seldom needed, and new syntax would break existing documents. When it's needed, the :superscript: (:sup:) role can be used as well.
Code ExecutionAdd the following directives?
"exec": Execute Python code & insert the results. Call it "python" to allow for other languages?
"system": Execute an os.system() call, and insert the results (possibly as a literal block). Definitely dangerous! How to make it safe? Perhaps such processing should be left outside of the document, in the user's production system (a makefile or a script or whatever). Or, the directive could be disabled by default and only enabled with an explicit command-line option or config file setting. Even then, an interactive prompt may be useful, such as:
The file.rst document you are processing contains a "system" directive requesting that the sudo rm -rf / command be executed. Allow it to execute? (y/N)
"eval": Evaluate an expression & insert the text. At parse time or at substitution time? Dangerous? Perhaps limit to canned macros; see text.date.
It's too dangerous (or too complicated in the case of "eval"). We do not want to have such things in the core.
encoding DirectiveAdd an "encoding" directive to specify the character encoding of the input data? Not a good idea for the following reasons:
When it sees the directive, the parser will already have read the input data, and encoding determination will already have been done.
If a file with an "encoding" directive is edited and saved with a different encoding, the directive may cause data corruption.
Add an "annotation" role, as the equivalent of the HTML "title" attribute? This is secondary information that may "pop up" when the pointer hovers over the main text. A corresponding directive would be required to associate annotations with the original text (by name, or positionally as in anonymous targets?).
There have not been many requests for such feature, though. [2] Also, cluttering WYSIWYG plaintext with annotations may not seem like a good idea, and there is no "tool tip" in formats other than HTML. [3]
Object referencesWe need syntax for object references.
Parameterized substitutions? For example:
See |figure (figure name)| on |page (figure name)|. .. |figure (name)| figure-ref:: (name) .. |page (name)| page-ref:: (name)The result would be:
See figure 3.11 on page 157.But this would require substitution directives to be processed at reference-time, not at definition-time as they are now. Or, perhaps the directives could just leave pending elements behind, and the transforms do the work? How to pass the data through? Too complicated. Use interpreted text roles.
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