428 lines
12 KiB
Markdown
428 lines
12 KiB
Markdown
# micromark-extension-math
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[![Build][build-badge]][build]
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[![Coverage][coverage-badge]][coverage]
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[![Downloads][downloads-badge]][downloads]
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[![Size][size-badge]][size]
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[![Sponsors][sponsors-badge]][collective]
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[![Backers][backers-badge]][collective]
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[![Chat][chat-badge]][chat]
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[micromark][] extensions to support math (`$C_L$`).
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## Contents
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* [What is this?](#what-is-this)
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* [When to use this](#when-to-use-this)
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* [Install](#install)
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* [Use](#use)
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* [API](#api)
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* [`math(options?)`](#mathoptions)
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* [`mathHtml(options?)`](#mathhtmloptions)
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* [`HtmlOptions`](#htmloptions)
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* [`Options`](#options)
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* [Authoring](#authoring)
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* [HTML](#html)
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* [CSS](#css)
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* [Syntax](#syntax)
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* [Types](#types)
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* [Compatibility](#compatibility)
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* [Security](#security)
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* [Related](#related)
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* [Contribute](#contribute)
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* [License](#license)
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## What is this?
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This package contains two extensions that add support for math syntax
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in markdown to [`micromark`][micromark].
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As there is no spec for math in markdown, this extension follows how code
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(fenced and text) works in Commonmark, but uses dollars.
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## When to use this
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This project is useful when you want to support math in markdown.
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Extending markdown with a syntax extension makes the markdown less portable.
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LaTeX equations are also quite hard.
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But this mechanism works well when you want authors, that have some LaTeX
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experience, to be able to embed rich diagrams of math in scientific text.
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You can use these extensions when you are working with [`micromark`][micromark]
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already.
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When you need a syntax tree, you can combine this package with
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[`mdast-util-math`][mdast-util-math].
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All these packages are used [`remark-math`][remark-math], which focusses on
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making it easier to transform content by abstracting these internals away.
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## Install
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This package is [ESM only][esm].
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In Node.js (version 16+), install with [npm][]:
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[npm][]:
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```sh
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npm install micromark-extension-math
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```
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In Deno with [`esm.sh`][esmsh]:
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```js
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import {math, mathHtml} from 'https://esm.sh/micromark-extension-math@3'
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```
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In browsers with [`esm.sh`][esmsh]:
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```html
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<script type="module">
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import {math, mathHtml} from 'https://esm.sh/micromark-extension-math@3?bundle'
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</script>
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```
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## Use
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Say our document `example.md` contains:
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```markdown
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Lift($L$) can be determined by Lift Coefficient ($C_L$) like the following equation.
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$$
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L = \frac{1}{2} \rho v^2 S C_L
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$$
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```
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…and our module `example.js` looks as follows:
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```js
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import fs from 'node:fs/promises'
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import {micromark} from 'micromark'
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import {math, mathHtml} from 'micromark-extension-math'
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const output = micromark(await fs.readFile('example.md'), {
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extensions: [math()],
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htmlExtensions: [mathHtml()]
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})
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console.log(output)
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```
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…now running `node example.js` yields (abbreviated):
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```html
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<p>Lift(<span class="math math-inline"><span class="katex">…</span></span>) can be determined by Lift Coefficient (<span class="math math-inline"><span class="katex">…</span></span>) like the following equation.</p>
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<div class="math math-display"><span class="katex-display"><span class="katex">…</span></span></div>
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```
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## API
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This package exports the identifiers [`math`][api-math] and
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[`mathHtml`][api-math-html].
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There is no default export.
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The export map supports the [`development` condition][development].
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Run `node --conditions development module.js` to get instrumented dev code.
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Without this condition, production code is loaded.
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### `math(options?)`
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Create an extension for `micromark` to enable math syntax.
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###### Parameters
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* `options` ([`Options`][api-options], default: `{}`)
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— configuration
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###### Returns
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Extension for `micromark` that can be passed in `extensions`, to enable math
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syntax ([`Extension`][micromark-extension]).
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### `mathHtml(options?)`
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Create an extension for `micromark` to support math when serializing to HTML.
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> 👉 **Note**: this uses KaTeX to render math.
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###### Parameters
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* `options` ([`HtmlOptions`][api-html-options], default: `{}`)
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— configuration
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###### Returns
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Extension for `micromark` that can be passed in `htmlExtensions`, to support
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math when serializing to HTML ([`HtmlExtension`][micromark-html-extension]).
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### `HtmlOptions`
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Configuration for HTML output (optional).
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> 👉 **Note**: passed to [`katex.renderToString`][katex-options].
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> `displayMode` is overwritten by this plugin, to `false` for math in text
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> (inline), and `true` for math in flow (block).
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###### Type
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```ts
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type Options = Omit<import('katex').KatexOptions, 'displayMode'>
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```
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### `Options`
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Configuration (TypeScript type).
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###### Fields
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* `singleDollarTextMath` (`boolean`, default: `true`)
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— whether to support math (text, inline) with a single dollar.
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Single dollars work in Pandoc and many other places, but often interfere
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with “normal” dollars in text.
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If you turn this off, you use two or more dollars for text math.
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## Authoring
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When authoring markdown with math, keep in mind that math doesn’t work in most
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places.
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Notably, GitHub currently has a really weird crappy client-side regex-based
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thing.
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But on your own (math-heavy?) site it can be great!
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You can use code (fenced) with an info string of `math` to improve this, as
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that works in many places.
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## HTML
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Math (flow) does not relate to HTML elements.
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`MathML`, which is sort of like SVG but for math, exists but it doesn’t work
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well and isn’t widely supported.
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Instead, this uses [KaTeX][], which generates MathML as a fallback but also
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generates a bunch of divs and spans so math look pretty.
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The KaTeX result is wrapped in `<div>` (for flow, block) and `<span>` (for text,
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inline) elements, with two classes: `math` and either `math-display` or
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`math-inline`.
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When turning markdown into HTML, each line ending in math (text) is turned
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into a space.
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## CSS
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The HTML produced by KaTeX requires CSS to render correctly.
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You should use `katex.css` somewhere on the page where the math is shown to
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style it properly.
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At the time of writing, the last version is:
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```html
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<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/katex@0.16.4/dist/katex.min.css">
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```
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## Syntax
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Math forms with the following BNF:
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```bnf
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; Restriction: the number of markers in the closing sequence must be equal
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; to the number of markers in the opening sequence.
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math_text ::= sequence_text 1*byte sequence_text
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math_flow ::= fence_open *( eol *line ) [ eol fence_close ]
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; Restriction: not preceded or followed by the marker.
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sequence_text ::= 1*'$'
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fence_open ::= sequence_flow meta
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; Restriction: the number of markers in the closing fence sequence must be
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; equal to or greater than the number of markers in the opening fence
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; sequence.
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fence_close ::= sequence_flow *space_or_tab
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sequence_flow ::= 2*'$'
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; Restriction: the marker cannot occur in `meta`
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meta ::= 1*line
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; Character groups for informational purposes.
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byte ::= 0x00..=0xFFFF
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eol ::= '\n' | '\r' | '\r\n'
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line ::= byte - eol
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```
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The above grammar shows that it is not possible to create empty math (text).
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It is possible to include the sequence marker (dollar) in math (text), by
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wrapping it in bigger or smaller sequences:
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```markdown
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Include more: $a$$b$ or include less: $$a$b$$.
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```
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It is also possible to include just one marker:
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```markdown
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Include just one: $$ $ $$.
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```
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Sequences are “gready”, in that they cannot be preceded or followed by more
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markers.
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To illustrate:
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```markdown
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Not math: $$x$.
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Not math: $x$$.
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Escapes work, this is math: \$$x$.
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Escapes work, this is math: $x$\$.
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```
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Yields:
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```html
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<p>Not math: $$x$.</p>
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<p>Not math: $x$$.</p>
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<p>Escapes work, this is math: $<span>…</span>.</p>
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<p>Escapes work, this is math: <span>…</span>$.</p>
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```
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That is because, when turning markdown into HTML, the first and last space,
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if both exist and there is also a non-space in the math, are removed.
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Line endings, at that stage, are considered as spaces.
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As the math (flow) construct occurs in flow, like all flow constructs, it must
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be followed by an eol (line ending) or eof (end of file).
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The above grammar does not show how indentation of each line is handled.
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To parse math (flow), let `x` be the number of `space_or_tab` characters
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before the opening fence sequence, after interpreting tabs based on how many
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virtual spaces they represent.
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Each line of text is then allowed (not required) to be indented with up
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to `x` spaces or tabs, which are then ignored as an indent instead of being
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considered as part of the content.
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This indent does not affect the closing fence.
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It can be indented up to a separate 3 real or virtual spaces.
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A bigger indent makes it part of the content instead of a fence.
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The `meta` part is interpreted as the [string][micromark-content-types] content
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type.
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That means that character escapes and character references are allowed.
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The optional `meta` part is ignored: it is not used when parsing or
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rendering.
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## Types
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This package is fully typed with [TypeScript][].
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It exports the additional types [`HtmlOptions`][api-html-options]
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and [`Options`][api-options].
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## Compatibility
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Projects maintained by the unified collective are compatible with maintained
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versions of Node.js.
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When we cut a new major release, we drop support for unmaintained versions of
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Node.
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This means we try to keep the current release line,
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`micromark-extension-math@^3`, compatible with Node.js 16.
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This package works with `micromark` version `3` and later.
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## Security
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This package is safe assuming that you trust KaTeX.
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Any vulnerability in it could open you to a [cross-site scripting (XSS)][xss]
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attack.
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## Related
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* [`remark-math`][remark-math]
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— remark (and rehype) plugins to support math
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* [`mdast-util-math`][mdast-util-math]
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— mdast utility to support math
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## Contribute
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See [`contributing.md` in `micromark/.github`][contributing] for ways to get
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started.
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See [`support.md`][support] for ways to get help.
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This project has a [code of conduct][coc].
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By interacting with this repository, organization, or community you agree to
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abide by its terms.
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## License
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[MIT][license] © [Titus Wormer][author]
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<!-- Definitions -->
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[build-badge]: https://github.com/micromark/micromark-extension-math/workflows/main/badge.svg
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[build]: https://github.com/micromark/micromark-extension-math/actions
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[coverage-badge]: https://img.shields.io/codecov/c/github/micromark/micromark-extension-math.svg
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[coverage]: https://codecov.io/github/micromark/micromark-extension-math
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[downloads-badge]: https://img.shields.io/npm/dm/micromark-extension-math.svg
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[downloads]: https://www.npmjs.com/package/micromark-extension-math
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[size-badge]: https://img.shields.io/badge/dynamic/json?label=minzipped%20size&query=$.size.compressedSize&url=https://deno.bundlejs.com/?q=micromark-extension-math
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[size]: https://bundlejs.com/?q=micromark-extension-math
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[sponsors-badge]: https://opencollective.com/unified/sponsors/badge.svg
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[backers-badge]: https://opencollective.com/unified/backers/badge.svg
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[collective]: https://opencollective.com/unified
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[chat-badge]: https://img.shields.io/badge/chat-discussions-success.svg
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[chat]: https://github.com/micromark/micromark/discussions
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[npm]: https://docs.npmjs.com/cli/install
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[esmsh]: https://esm.sh
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[license]: license
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[author]: https://wooorm.com
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[contributing]: https://github.com/micromark/.github/blob/main/contributing.md
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[support]: https://github.com/micromark/.github/blob/main/support.md
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[coc]: https://github.com/micromark/.github/blob/main/code-of-conduct.md
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[esm]: https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c
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[typescript]: https://www.typescriptlang.org
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[development]: https://nodejs.org/api/packages.html#packages_resolving_user_conditions
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[micromark]: https://github.com/micromark/micromark
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[micromark-content-types]: https://github.com/micromark/micromark#content-types
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[micromark-html-extension]: https://github.com/micromark/micromark#htmlextension
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[micromark-extension]: https://github.com/micromark/micromark#syntaxextension
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[mdast-util-math]: https://github.com/syntax-tree/mdast-util-math
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[remark-math]: https://github.com/remarkjs/remark-math
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[katex]: https://katex.org
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[katex-options]: https://katex.org/docs/options.html
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[xss]: https://en.wikipedia.org/wiki/Cross-site_scripting
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[api-math]: #mathoptions
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[api-math-html]: #mathhtmloptions
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[api-options]: #options
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[api-html-options]: #htmloptions
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