Markdown Abstract Syntax Tree.
mdast is a specification for representing markdown in a syntax tree. It implements unist. It can represent several flavours of markdown, such as CommonMark and GitHub Flavored Markdown.
This document may not be released.
See releases for released documents.
The latest released version is 5.0.0.
- Introduction
- Types
- Nodes (abstract)
- Nodes
- Mixin
- Enumeration
- Content model
- Extensions
- Glossary
- List of utilities
- References
- Security
- Related
- Contribute
- Acknowledgments
- License
This document defines a format for representing markdown as an abstract syntax tree. Development of mdast started in July 2014, in remark, before unist existed. This specification is written in a Web IDL-like grammar.
mdast extends unist, a format for syntax trees, to benefit from its ecosystem of utilities.
mdast relates to JavaScript in that it has a rich ecosystem of utilities for working with compliant syntax trees in JavaScript. However, mdast is not limited to JavaScript and can be used in other programming languages.
mdast relates to the unified and remark projects in that mdast syntax trees are used throughout their ecosystems.
If you are using TypeScript, you can use the unist types by installing them with npm:
npm install @types/mdastinterface Literal <: UnistLiteral {
value: string
}Literal (UnistLiteral) represents an abstract interface in mdast containing a value.
Its value field is a string.
interface Parent <: UnistParent {
children: [MdastContent]
}Parent (UnistParent) represents an abstract interface in mdast containing other nodes (said to be children).
Its content is limited to only other mdast content.
interface Blockquote <: Parent {
type: 'blockquote'
children: [FlowContent]
}Blockquote (Parent) represents a section quoted from somewhere else.
Blockquote can be used where flow content is expected. Its content model is also flow content.
For example, the following markdown:
> Alpha bravo charlie.Yields:
{
type: 'blockquote',
children: [{
type: 'paragraph',
children: [{type: 'text', value: 'Alpha bravo charlie.'}]
}]
}interface Break <: Node {
type: 'break'
}Break (Node) represents a line break, such as in poems or addresses.
Break can be used where phrasing content is expected. It has no content model.
For example, the following markdown:
foo··
barYields:
{
type: 'paragraph',
children: [
{type: 'text', value: 'foo'},
{type: 'break'},
{type: 'text', value: 'bar'}
]
}interface Code <: Literal {
type: 'code'
lang: string?
meta: string?
}Code (Literal) represents a block of preformatted text, such as ASCII art or computer code.
Code can be used where flow content is expected.
Its content is represented by its value field.
This node relates to the phrasing content concept InlineCode.
A lang field can be present.
It represents the language of computer code being marked up.
If the lang field is present,
a meta field can be present.
It represents custom information relating to the node.
For example, the following markdown:
foo()Yields:
{
type: 'code',
lang: null,
meta: null,
value: 'foo()'
}And the following markdown:
```js highlight-line="2"
foo()
bar()
baz()
```Yields:
{
type: 'code',
lang: 'javascript',
meta: 'highlight-line="2"',
value: 'foo()\nbar()\nbaz()'
}interface Definition <: Node {
type: 'definition'
}
Definition includes Association
Definition includes ResourceDefinition (Node) represents a resource.
Definition can be used where content is expected. It has no content model.
Definition includes the mixins Association and Resource.
Definition should be associated with LinkReferences and ImageReferences.
For example, the following markdown:
[Alpha]: https://example.comYields:
{
type: 'definition',
identifier: 'alpha',
label: 'Alpha',
url: 'https://example.com',
title: null
}interface Emphasis <: Parent {
type: 'emphasis'
children: [PhrasingContent]
}Emphasis (Parent) represents stress emphasis of its contents.
Emphasis can be used where phrasing content is expected. Its content model is phrasing content.
For example, the following markdown:
*alpha* _bravo_Yields:
{
type: 'paragraph',
children: [
{
type: 'emphasis',
children: [{type: 'text', value: 'alpha'}]
},
{type: 'text', value: ' '},
{
type: 'emphasis',
children: [{type: 'text', value: 'bravo'}]
}
]
}interface Heading <: Parent {
type: 'heading'
depth: 1 <= number <= 6
children: [PhrasingContent]
}Heading (Parent) represents a heading of a section.
Heading can be used where flow content is expected. Its content model is phrasing content.
A depth field must be present.
A value of 1 is said to be the highest rank and 6 the lowest.
For example, the following markdown:
# AlphaYields:
{
type: 'heading',
depth: 1,
children: [{type: 'text', value: 'Alpha'}]
}interface Html <: Literal {
type: 'html'
}Html (Literal) represents a fragment of raw HTML.
Html can be used where flow or
phrasing content is expected.
Its content is represented by its value field.
Html nodes do not have the restriction of being valid or complete HTML ([HTML]) constructs.
For example, the following markdown:
<div>Yields:
{type: 'html', value: '<div>'}interface Image <: Node {
type: 'image'
}
Image includes Resource
Image includes AlternativeImage (Node) represents an image.
Image can be used where phrasing content is
expected.
It has no content model,
but is described by its alt field.
Image includes the mixins Resource and Alternative.
For example, the following markdown:
Yields:
{
type: 'image',
url: 'https://example.com/favicon.ico',
title: 'bravo',
alt: 'alpha'
}interface ImageReference <: Node {
type: 'imageReference'
}
ImageReference includes Reference
ImageReference includes AlternativeImageReference (Node) represents an image through association, or its original source if there is no association.
ImageReference can be used where phrasing
content is expected.
It has no content model,
but is described by its alt field.
ImageReference includes the mixins Reference and Alternative.
ImageReference should be associated with a Definition.
For example, the following markdown:
![alpha][bravo]Yields:
{
type: 'imageReference',
identifier: 'bravo',
label: 'bravo',
referenceType: 'full',
alt: 'alpha'
}interface InlineCode <: Literal {
type: 'inlineCode'
}InlineCode (Literal) represents a fragment of computer code, such as a file name, computer program, or anything a computer could parse.
InlineCode can be used where phrasing content
is expected.
Its content is represented by its value field.
This node relates to the flow content concept Code.
For example, the following markdown:
`foo()`Yields:
{type: 'inlineCode', value: 'foo()'}interface Link <: Parent {
type: 'link'
children: [PhrasingContent]
}
Link includes ResourceLink (Parent) represents a hyperlink.
Link can be used where phrasing content is expected. Its content model is also phrasing content.
Link includes the mixin Resource.
For example, the following markdown:
[alpha](https://example.com "bravo")Yields:
{
type: 'link',
url: 'https://example.com',
title: 'bravo',
children: [{type: 'text', value: 'alpha'}]
}interface LinkReference <: Parent {
type: 'linkReference'
children: [PhrasingContent]
}
LinkReference includes ReferenceLinkReference (Parent) represents a hyperlink through association, or its original source if there is no association.
LinkReference can be used where phrasing content is expected. Its content model is also phrasing content.
LinkReference includes the mixin Reference.
LinkReferences should be associated with a Definition.
For example, the following markdown:
[alpha][Bravo]Yields:
{
type: 'linkReference',
identifier: 'bravo',
label: 'Bravo',
referenceType: 'full',
children: [{type: 'text', value: 'alpha'}]
}interface List <: Parent {
type: 'list'
ordered: boolean?
start: number?
spread: boolean?
children: [ListContent]
}List (Parent) represents a list of items.
List can be used where flow content is expected. Its content model is list content.
An ordered field can be present.
It represents that the items have been intentionally ordered (when true),
or that the order of items is not important (when false or not present).
A start field can be present.
It represents,
when the ordered field is true,
the starting number of the list.
A spread field can be present.
It represents that one or more of its children are separated with a blank line
from its siblings (when true),
or not (when false or not present).
For example, the following markdown:
1. fooYields:
{
type: 'list',
ordered: true,
start: 1,
spread: false,
children: [{
type: 'listItem',
spread: false,
children: [{
type: 'paragraph',
children: [{type: 'text', value: 'foo'}]
}]
}]
}interface ListItem <: Parent {
type: 'listItem'
spread: boolean?
children: [FlowContent]
}ListItem (Parent) represents an item in a List.
ListItem can be used where list content is expected. Its content model is flow content.
A spread field can be present.
It represents that the item contains two or more children
separated by a blank line (when true),
or not (when false or not present).
For example, the following markdown:
* barYields:
{
type: 'listItem',
spread: false,
children: [{
type: 'paragraph',
children: [{type: 'text', value: 'bar'}]
}]
}interface Paragraph <: Parent {
type: 'paragraph'
children: [PhrasingContent]
}Paragraph (Parent) represents a unit of discourse dealing with a particular point or idea.
Paragraph can be used where content is expected. Its content model is phrasing content.
For example, the following markdown:
Alpha bravo charlie.Yields:
{
type: 'paragraph',
children: [{type: 'text', value: 'Alpha bravo charlie.'}]
}interface Root <: Parent {
type: 'root'
}Root (Parent) represents a document.
Root can be used as the root of a tree, never as a child. Its content model is not limited to flow content, but instead can contain any mdast content with the restriction that all content must be of the same category.
interface Strong <: Parent {
type: 'strong'
children: [PhrasingContent]
}Strong (Parent) represents strong importance, seriousness, or urgency for its contents.
Strong can be used where phrasing content is expected. Its content model is phrasing content.
For example, the following markdown:
**alpha** __bravo__Yields:
{
type: 'paragraph',
children: [
{
type: 'strong',
children: [{type: 'text', value: 'alpha'}]
},
{type: 'text', value: ' '},
{
type: 'strong',
children: [{type: 'text', value: 'bravo'}]
}
]
}interface Text <: Literal {
type: 'text'
}Text (Literal) represents everything that is just text.
Text can be used where phrasing content is
expected.
Its content is represented by its value field.
For example, the following markdown:
Alpha bravo charlie.Yields:
{type: 'text', value: 'Alpha bravo charlie.'}interface ThematicBreak <: Node {
type: 'thematicBreak'
}ThematicBreak (Node) represents a thematic break, such as a scene change in a story, a transition to another topic, or a new document.
ThematicBreak can be used where flow content is expected. It has no content model.
For example, the following markdown:
***Yields:
{type: 'thematicBreak'}interface mixin Alternative {
alt: string?
}Alternative represents a node with a fallback
An alt field should be present.
It represents equivalent content for environments that cannot represent the
node as intended.
interface mixin Association {
identifier: string
label: string?
}Association represents an internal relation from one node to another.
An identifier field must be present.
It can match another node.
identifier is a source value: character escapes and character references are
not parsed.
Its value must be normalized.
A label field can be present.
label is a string value: it works just like title on a link or a lang on
code: character escapes and character references are parsed.
To normalize a value,
collapse markdown whitespace ([\t\n\r ]+) to a space,
trim the optional initial and/or final space,
and perform case-folding.
Whether the value of identifier (or normalized label if there is no
identifier) is expected to be a unique identifier or not depends on the type
of node including the Association.
An example of this is that they should be unique on
Definition,
whereas multiple LinkReferences can be non-unique to
be associated with one definition.
interface mixin Reference {
referenceType: string
}
Reference includes AssociationReference represents a marker that is associated to another node.
A referenceType field must be present.
Its value must be a referenceType.
It represents the explicitness of the reference.
interface mixin Resource {
url: string
title: string?
}Resource represents a reference to resource.
A url field must be present.
It represents a URL to the referenced resource.
A title field can be present.
It represents advisory information for the resource,
such as would be appropriate for a tooltip.
enum referenceType {
'shortcut' | 'collapsed' | 'full'
}referenceType represents the explicitness of a reference.
- shortcut: the reference is implicit, its identifier inferred from its content
- collapsed: the reference is explicit, its identifier inferred from its content
- full: the reference is explicit, its identifier explicitly set
type MdastContent = FlowContent | ListContent | PhrasingContentEach node in mdast falls into one or more categories of Content that group nodes with similar characteristics together.
type Content = Definition | ParagraphContent represents runs of text that form definitions and paragraphs.
type FlowContent =
Blockquote | Code | Heading | Html | List | ThematicBreak | ContentFlow content represent the sections of document.
type ListContent = ListItemList content represent the items in a list.
type PhrasingContent = Break | Emphasis | Html | Image | ImageReference
| InlineCode | Link | LinkReference | Strong | TextPhrasing content represent the text in a document and its markup.
Markdown syntax is often extended. It is not a goal of this specification to list all possible extensions. However, a short list of frequently used extensions are shown below.
The following interfaces are found in GitHub Flavored Markdown.
interface Delete <: Parent {
type: 'delete'
children: [PhrasingContent]
}Delete (Parent) represents contents that are no longer accurate or no longer relevant.
Delete can be used where phrasing content is expected. Its content model is phrasing content.
For example, the following markdown:
~~alpha~~Yields:
{
type: 'delete',
children: [{type: 'text', value: 'alpha'}]
}interface ListItemGfm <: ListItem {
checked: boolean?
}In GFM,
a checked field can be present.
It represents whether the item is done (when true),
not done (when false),
or indeterminate or not applicable (when null or not present).
interface FootnoteDefinition <: Parent {
type: 'footnoteDefinition'
children: [FlowContent]
}
FootnoteDefinition includes AssociationFootnoteDefinition (Parent) represents content relating to the document that is outside its flow.
FootnoteDefinition can be used where flow content is expected. Its content model is also flow content.
FootnoteDefinition includes the mixin Association.
FootnoteDefinition should be associated with FootnoteReferences.
For example, the following markdown:
[^alpha]: bravo and charlie.Yields:
{
type: 'footnoteDefinition',
identifier: 'alpha',
label: 'alpha',
children: [{
type: 'paragraph',
children: [{type: 'text', value: 'bravo and charlie.'}]
}]
}
