My RSS feed was broken for OVER A WEEK because I used an invalid character in the XML.
I use a GitHub action to update my GitHub profile README with my latest blog posts. For over a week the job had been failing, and I ignored it (rookie mistake). It turns out I had broken my RSS feed when I edited some blog post descriptions and used a character that wasn't valid in XML (referred to as an invalid token).
The error in the GitHub action workflow run wasn't very helpful, though: "Error: Invalid character in entity name".
Luckily, the RSS Feed Validation Service provided by W3C gave a better error report.
This helped me track down the invalid character to an ampersand (&), which I added to a blog post description a week ago to reduce the character count. The resulting invalid description tag in the XML document looked like this:
<title>When to use aria-labels in your HTML</title>
<description>This is one of the most important ways to use aria-labels so your code provides contextual information to screen-readers & assistive tech.
I did some further reading on XML and learned that ampersands, and left and right angled brackets (< and >) must be escaped in XML in order for the document to be valid, unless wrapped in a CDATA section. Read more about XML character data and markup on the official W3C docs.