Warns that attributes were duplicated in one element. Capital letters and lower-case letters are not distinguished.
There must never be two or more attributes on the same start tag whose names are an ASCII case-insensitive match for each other.
❌ Examples of incorrect code for this rule
<div data-attr="value" data-Attr="db"></div>
✅ Examples of correct code for this rule
<div data-attr="value" data-Attr2="db"></div>