Project: syntax-tree/mdast-zone

Package: mdast-zone@5.1.0

  1. Dependents: 0
  2. mdast utility to treat HTML comments as ranges or markers
  1. util 145
  2. utility 141
  3. unist 132
  4. html 124
  5. mdast 88
  6. mdast-util 30
  7. marker 13
  8. comment 9
  9. range 2


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mdast utility to find two comments and replace the content in them.


What is this?

This package is a utility that lets you find certain comments, then takes the content between them, and calls a given handler with the result, so that you can change or replace things.

When should I use this?

This utility is typically useful when you have certain sections that can be generated. Comments are a hidden part of markdown, so they can be used as processing instructions. You can use those comments to define what content to change or replace.

A similar package, mdast-util-heading-range, does the same but uses a heading to mark the start and end of sections.


This package is ESM only. In Node.js (version 16+), install with npm:

npm install mdast-zone

In Deno with esm.sh:

import {zone} from 'https://esm.sh/mdast-zone@6'

In browsers with esm.sh:

<script type="module">
  import {zone} from 'https://esm.sh/mdast-zone@6?bundle'


Say we have the following file, example.md:

<!--foo start-->


<!--foo end-->

…and a module example.js:

import {zone} from 'mdast-zone'
import {remark} from 'remark'
import {read} from 'to-vfile'

const file = await remark()
  .process(await read('example.md'))


/** @type {import('unified').Plugin<[], import('mdast').Root>} */
function myPluginThatReplacesFoo() {
  return function (tree) {
    zone(tree, 'foo', function (start, nodes, end) {
      return [
        {type: 'paragraph', children: [{type: 'text', value: 'Bar.'}]},

…now running node example.js yields:

<!--foo start-->


<!--foo end-->


This package exports the identifier zone. There is no default export.

zone(tree, name, handler)

Search tree for a start and end comments matching name and change their “section” with handler.


Nothing (undefined).


Callback called when a section is found (TypeScript type).


Results (Array<Node | null | undefined>, optional).

If nothing is returned, nothing will be changed. If an array of nodes (can include null and undefined) is returned, the original section will be replaced by those nodes.


Extra info (TypeScript type).



This package is fully typed with TypeScript. It exports the additional types Handler and Info.


Projects maintained by the unified collective are compatible with maintained versions of Node.js.

When we cut a new major release, we drop support for unmaintained versions of Node. This means we try to keep the current release line, mdast-zone@^6, compatible with Node.js 16.


Improper use of handler can open you up to a cross-site scripting (XSS) attack as the value it returns is injected into the syntax tree. This can become a problem if the tree is later transformed to hast. The following example shows how a script is injected that could run when loaded in a browser.

function handler(start, nodes, end) {
  return [start, {type: 'html', value: '<script>alert(1)</script>'}, end]


<!--foo start-->


<!--foo end-->

Either do not use user input or use hast-util-santize.


See contributing.md in syntax-tree/.github for ways to get started. See support.md for ways to get help.

This project has a code of conduct. By interacting with this repository, organization, or community you agree to abide by its terms.


MIT © Titus Wormer