pve-docs/debian/tree/pve-docs-mediawiki/PVEDocs/include/PVEDocs.php

<?php
// see http://www.mediawiki.org/wiki/Manual:Parser_functions

class PVEDocs {
    public static function onParserFirstCallInit(Parser $parser ) {
        $parser->setFunctionHook('pvedocs', [ self::class, 'efPvedocsParserFunction_Render' ]);
        $parser->setHook('pvehide',  [ self::class, 'renderTagPveHideContent' ]);

        return true;
    }

    // similar code as in <htmlet> tag...
    public static function efPvedocsPostProcessFunction($parser, &$text) {
        $text = preg_replace_callback(
            '/<!--- @PVEDOCS_BASE64@ ([0-9a-zA-Z\\+\\/]+=*) @PVEDOCS_BASE64@ -->/sm',
            function ($m) { return base64_decode("$m[1]"); },
                $text
        );
        return true;
    }

    // "Render" <pvehide>
    public static function renderTagPveHideContent($input, array $args, Parser $parser, PPFrame $frame ) {
        return ''; // simply return nothing
    }


    # Render the output of {{#pvedocs:chapter}}.
    public static function efPvedocsParserFunction_Render(Parser $parser, $doc = '') {
        $parser->getOutput()->updateCacheExpiry(0); // disableCache() was dropped in MW 1.34

        // only allow simple names, so that jist files from within "/usr/share/pve-docs/" can be included
        if (!preg_match("/[a-z0-9.-]+\.html/i", $doc)) {
            die("no such manual page");
        }

        $content = file_get_contents("/usr/share/pve-docs/$doc");

        // from https://gerrit.wikimedia.org/r/plugins/gitiles/mediawiki/extensions/HTMLets/+/11e5ef1ea2820319458dc67174ca76d6e00b10cc/HTMLets.php#140
        $output = '<!--- @PVEDOCS_BASE64@ '.base64_encode($content).' @PVEDOCS_BASE64@ -->';
        return array($output, 'noparse' => true, 'isHTML' => true);
    }
}