Examples
PHP Manual

Output rewrite usage

Since PHP 7.1.0, output_add_rewrite_var, output_reset_rewrite_vars use dedicated output buffer. i.e. It does not use trans sid output buffer.

Example #1 Output rewrite example

<?php
// This code works with PHP 7.1.0, 7.0.10, 5.6.25 and up.

// HTTP_HOST is default target host. Set manually to make sample code works.
$_SERVER['HTTP_HOST'] = 'php.net';

// Output rewriter only rewrite form. Add a=href.
// Tags can be specified tag_name=url_attr, e.g. img=src,iframe=src
// No space allowed between settings.
// Form tag is special tag that add hidden input.
ini_set('url_rewriter.tags','a=href,form=');
var_dump(ini_get('url_rewriter.tags'));

// This is added to URL and form
output_add_rewrite_var('test', 'value');
?>
<a href="//php.net/index.php?bug=1234">bug1234</a>
<form action="https://php.net/?bug=1234&edit=1" method="post">
 <input type="text" name="title" />
</form>

The above example will output:

<a href="//php.net/?bug=1234&test=value">bug1234</a>
<form action="https://php.net/?bug=1234&edit=1" method="post"><input type="hidden" name="test" value="value" />
 <input type="text" name="title" />
</form>

Since PHP 7.1.0, output rewrite functions have it's own INI settings, url_rewriter.tags and url_rewriter.hosts.