Rocket Validator integrates the W3C Validator HTML checker into an automated web crawler.
HTML issues tagged as matching.
Quote characters used for attributes can use either single quotes (') or double quotes ("), and they must be properly matched, for example:
A common cause for this issue is forgetting to use the equal sign (=), so the HTML parser wrongly believes the quote forms part of the attribute name, for example:
<p class "news">this is wrong</p>
When was the last time you validated your whole site?
Keep your sites healthy checking for A11Y/HTML issues on an automated schedule.