Bug Description

The plugin implements the removal of unused CSS rules on the page. This works well for all page content, including <template type="amp-mustache">...</template>, but does not work with <script type="text/plain" template="amp-mustache">...</script>.

Expected Behaviour

Preserve CSS rules for elements inside <script type="text/plain" template="amp-mustache">...</script>.

Steps to reproduce

1. Add code to AMP page:

<style>
    h2.one { color: green }
    h2.two { color: red }
</style>
<template type="amp-mustache">
    <h2 class="one">One</h2>
</template>
<script type="text/plain" template="amp-mustache">
    <h2 class="two">Two</h2>
</script>

2. View the resulting source code for an AMP page.
3. See content <style amp-custom>...</style> in page head where there is a rule h2.one{color:green} but there is no rule h2.two{color:red}.

Additional context

• WordPress version: 5.3.2
• Plugin version: 1.4.2
• AMP plugin template mode: Website; Standard; Serve all templates as AMP regardless of what is being queried.
• PHP version: 7.3.11

Acceptance criteria

Implementation brief

QA testing instructions

Demo

Changelog entry