Add Readme.md

Author: wooorm

Readme.md

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+# ![NLCST](http://wooorm.com/nlcst.png)
+
+Natural language for human and machine.
+
+---
+
+> Note: Several projects use this document. Do not make changes without consulting with [TextOM](https://github.com/wooorm/textom),  [parse-latin](https://github.com/wooorm/parse-latin), and [retext](https://github.com/wooorm/retext).
+
+## CST
+
+### Node
+
+Node represents any unit in NLCST hierarchy.
+
+```
+interface Node {
+    type: string;
+    data: Data | null;
+}
+```
+
+### Data
+
+Data represents data associated with any node. Data is a scope for plug-ins to store any information. Its only limitation being that each property should by stringifyable: not throw when passed to `JSON.stringify()`.
+
+```
+interface Data { }
+```
+
+### Parent
+
+Parent ([Node](#node)) represents a unit in NLCST hierarchy which can have zero or more children.
+
+```
+interface Parent <: Node {
+    children: [];
+}
+```
+
+### Text
+
+Text ([Node](#node)) represents a unit in NLCST hierarchy which has value.
+
+```
+interface Text <: Node {
+    value: string;
+}
+```
+
+### RootNode
+
+Root ([Parent](#parent)) represents a document.
+
+```
+interface RootNode < Parent {
+    type: "RootNode";
+}
+```
+
+### ParagraphNode
+
+Paragraph ([Parent](#parent)) represents a self-contained unit of discourse in writing dealing with a particular point or idea.
+
+```
+interface ParagraphNode < Parent {
+    type: "ParagraphNode";
+}
+```
+
+### SentenceNode
+
+Sentence ([Parent](#parent)) represents grouping of grammatically linked words, that in principle tells a complete thought, although it may make little sense taken in isolation out of context.
+
+```
+interface SentenceNode < Parent {
+    type: "SentenceNode";
+}
+```
+
+### WordNode
+
+Word ([Parent](#parent)) represents the smallest element that may be uttered in isolation with semantic or pragmatic content.
+
+```
+interface WordNode < Parent {
+    type: "WordNode";
+}
+```
+
+### PunctuationNode
+
+Punctuation ([Parent](#parent)) represents typographical devices which aids understanding and correct reading of other grammatical units.
+
+```
+interface PunctuationNode < Parent {
+    type: "PunctuationNode";
+}
+```
+
+### WhiteSpaceNode
+
+White Space ([PunctuationNode](#punctuation)) represents typographical devices devoid of content, separating other grammatical units.
+
+```
+interface WhiteSpaceNode < PunctuationNode {
+    type: "WhiteSpaceNode";
+}
+```
+
+### SourceNode
+
+Source ([Text](#text)) represents an external (ungrammatical) value embedded into a grammatical unit: a hyperlink, an emoticon, and such.
+
+```
+interface SourceNode < Text {
+    type: "SourceNode";
+}
+```
+
+### TextNode
+
+Text ([Text](#text)) represents actual content in an NLCST document: one or more characters.
+
+```
+interface TextNode < Text {
+    type: "TextNode";
+}
+```
+
+## Related
+
+- [retext](https://github.com/wooorm/retext) — Analyse and Manipulate natural language, 20+ plug-ins.
+- [parse-latin](https://github.com/wooorm/parse-latin) — Transforms latin-script natural language into a CST;
+- [TextOM](https://github.com/wooorm/textom) — Provides an object-oriented manipulation interface to NLCST;
+- [nlcst-to-string](https://github.com/wooorm/nlcst-to-string) — Transforms a CST into a string;
+
+## License
+
+MIT © Titus Wormer