Extension points

Choose the narrowest extension contract that owns the required behavior. Alto compiles all registered definitions when the factory is created.

Registration

with() returns a new factory and leaves the original unchanged:

<?php
use Alto\Markdown\Extension\HeadingPermalink\HeadingPermalinkExtension;
use Alto\Markdown\Markdown;

$base = Markdown::github();
$extended = $base->with(new HeadingPermalinkExtension());

Extension names and local definition names form qualified node kinds such as acme:callout. Definitions with invalid names, reserved parser triggers, or conflicting contracts fail while the profile is compiled.

Trust boundary

Extensions are PHP code and therefore trusted. HTML callbacks must escape dynamic values through their output context. Source transforms must return validated patches. Resource behavior must receive explicit authority from the application.

See Custom extension for a complete small metric and Compatibility for the public versioning boundary.