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# ![Unist][logo]
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**Unist** (**uni**versal **s**yntax **t**ree) is the combination of three
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project, and more to come, which are the summation of at least
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[two][first-retext-commit] [years][first-remark-commit] of my work and the
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current epitome of that.
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**Uni**versal **S**yntax **T**ree.
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***
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**Unist** is the combination of three project, and more to come, which
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are the summation of at least [two][first-retext-commit]
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[years][first-remark-commit] of my work and the current epitome of that.
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It’s basically a system for processing input: parsing it into a syntax tree,
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transforming it by plug-ins, and compiling the tree to something else.
@@ -13,32 +16,86 @@ This document explains some terminology relating to [**retext**][retext],
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## Unist nodes
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**Unist nodes**:
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* must have a `type` property set to a to its namespace semantic
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`string`;
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* may have either a `value` property set to a `string` or a `children`
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property set to an array of zero or more `Unist` nodes;
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* may have a `data` property set to a `JSON.stringify`able object;
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* may have a `position` property set to a an object containing `start` and
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`end`, both of which contain an object with `line` and `column` set
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to an integer referencing their respective (1-based) line and column
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in the input file. Both may have an `offset` property set to its
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index from the beginning of the input.
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The object at `position` may additionally have an `indent` property
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set to an array of integers higher than 0 (not including), in which
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case the node represents content which spans multiple lines prefixed
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with content which is not part of the node.
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If a node represents something not available in the original input, it
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must not have a `position`.
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See [**nlcst**][nlcst] for more information on **retext** nodes,
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[**mdast**][mdast] for information on **remark** nodes, and
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[`hast#nodes`][hast-nodes] for information on **hast** nodes.
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### `Node`
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Node represents any unit in the Unist hierarchy. It is an abstract
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class. Interfaces inheriting from **Node** must have a `type` property,
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and may have `data` or `location` properties. `type`s are defined by
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their namespace.
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```idl
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interface Node {
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type: string;
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data: Data?;
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position: Location?;
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}
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```
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#### `Data`
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Data represents data associated with any node. Data is a scope for plug-ins
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to store any information. Its only limitation being that each property should
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by `stringify`able: not throw when passed to `JSON.stringify()`.
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```idl
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interface Data { }
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```
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#### `Location`
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**Location** references a location of a node in a **Unist** file.
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If a location is not applicable, the location must be omitted.
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**Location** consists of a `start` and end `position`. And, if
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relevant, an `indent` property.
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```idl
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interface Location {
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start: Position;
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end: Position;
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indent: [uint32 >= 1]?;
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}
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```
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#### `Position`
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**Position** contains `line` and `column` set to a (1-based) integer
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referencing a position in a **Unist** file. An `offset` (0-based)
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may be used.
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```idl
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interface Position {
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line: uint32 >= 1;
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column: uint32 >= 1;
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offset: uint32 >= 0?;
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}
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```
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### `Parent`
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Nodes containing child nodes inherit the **Parent** ([**Node**](#node))
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abstract interface.
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```idl
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interface Parent <: Node {
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children: [Node];
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}
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```
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### `Text`
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Nodes containing a value inherit the **Text** ([**Node**](#node))
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abstract interface.
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```idl
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interface Text <: Node {
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value: string;
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}
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```
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## Unist files
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**Unist files** are virtual files (such as [**vfile**][vfile])
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