cradeq/commonmark-strikethrough-sub-sup-extension

Adds support for strikethrough, subscript and superscript in Markdown (using `<del>`, `<sub>` and `<sup>` HTML tags).

v1.0.0 2026-02-10 20:24 UTC

Requires

• php: ^8.0
• league/commonmark: ^2.8

Requires (Dev)

• phpunit/phpunit: ^13.0

MIT

• markdown
• extension
• sub
• subscript
• commonmark
• strikethrough
• sup
• superscript
• tilde

README

This package adds support for subscript and superscript in Markdown (using <sub> and <sup> HTML tags). This package also duplicates the logic used in the League Strikethrough Extension (which generates <del> tags).

There is no official spec that supports both subscript and strikethrough. As they both typically use the tilde character (~), we follow the extended syntax of Markdown Guide. That means that strikethrough with only one tilde is necessarily NOT supported. Subscript and strikethrough can be nested, similar to how emphasis works (~Subscript ~~Subscript and striked~~~).

Added markdown features

Name	Markdown	Result
Superscript	^Text^	<sup>Text</sup>
Subscript	~Text~	<sub>Text</sub>
Strikethrough	~~Text~~	<del>Text</del>

Install

This project can be installed via composer:

composer require cradeq/commonmark-strikethrough-sub-sup-extension

Usage

use Cradeq\CommonMark\StrikethroughSubExtension;
use Cradeq\CommonMark\SupExtension;
use League\CommonMark\Environment\Environment;
use League\CommonMark\Extension\CommonMark\CommonMarkCoreExtension;

$environment = new Environment();
$environment->addExtension(new CommonMarkCoreExtension);
$environment->addExtension(new StrikethroughSubExtension);
$environment->addExtension(new SupExtension);