Unescaped '<' not allowed in attributes values
A < character inside an attribute value.
The message, as the validator reports it
Unescaped '<' not allowed in attributes values
Why it happens
- A comparison or markup kept in an attribute:
test="a < b",title="<b>bold</b>". - A missing closing quote on the previous attribute, so the next tag seems to be inside the value.
How to fix it
Write < instead of < inside attribute values. If the cause is a missing quote, the line of the error is usually just after it.
Example
Reports the error
<rule test="a < b"/>
Fixed
<rule test="a < b"/>