Unknown properties

[LeaVerou]

This could include:

• Most common invalid (nonexistent) properties, at-rules, selectors
• Common syntax errors

[LeaVerou]

Algorithm for nonexistent properties:

Properties that are not:

• known properties, possibly run in a variety of browsers and merge results
• Prefixed properties. For simplicity, let's just assume everything prefixed with -webkit-, -moz-, -ms-, -apple-, -o- is valid
• Custom properties (beginning with --)

For syntax errors that we can actually detect via the AST, all I can think of is missing semicolons, where a property value contains propertyName:. Any others?

[LeaVerou]

I decided to only do nonexistent properties, as the other one with the semicolon would yield too many false positives to be interesting.