Unexpected AMP validation error when aria-label contains >

[westonruter]

When adding this paragraph block:

<!-- wp:paragraph -->
<p>In 'Classic' template mode, you can use the&nbsp;<a href="https://github.com/Automattic/amp-wp/blob/1b3bf237993de37eaa19be86d500a61e49759421/includes/admin/functions.php#L161" target="_blank" rel="noreferrer noopener" aria-label="In 'Classic' template mode, you can use the&nbsp;amp_post_template_analytics&nbsp;filter. This template mode is set either from selecting 'Classic' in 'AMP Settings' > 'Template Mode,' or from not calling&nbsp;add_theme_support( 'amp' ). (opens in a new tab)">amp_post_template_analytics</a>&nbsp;filter. This template mode is set either from selecting 'Classic' in 'AMP Settings' &gt; 'Template Mode,' or from not calling&nbsp;<code>add_theme_support( 'amp' )</code>.</p>
<!-- /wp:paragraph -->

AN unexpected validation error occurs:

I thought this was related to WordPress/gutenberg#8779 but apparently not. It appears the source stack comment is somehow being incorrectly injected into the attribute value. In Gutenberg, the issue would probably be fixed if > could be replaced with > but every time this is manually fixed, the block serializer re-encodes as >. I thought that such characters were supposed to be encoded in WordPress/gutenberg#9963. Nevertheless, since < and > are allowed in attribute values, the validator should be resilient to them being present irrespective of Gutenberg.

[westonruter]

I don't think there is anything we can do here. It's an issue with Gutenberg's block serializer which should encode > as > and it's also an issue with wptexturize() erroneously converting attribute-closing " to #8243;. See WordPress/gutenberg#9963 (comment) and now WordPress/gutenberg#15636.

Quick fix is to remove < and > from attribute values inside the_content.