Added CONTRIBUTING.md.
Fix jQuery #13894: CSS identifiers with backslash-escaped whitespace
Fix jQuery #13936: iframe reload should not affect Sizzle. Close gh-213.
Fix jQuery #13974: Screen XML documents from special attrHandle processing
No ticket: Save 40 bytes
No ticket: Remove non-ASCII characters
Simplify XML checks. +0 bytes.
Update inline docs
Remove internal isNative function. -10 bytes.
Don't use frameElement property. Fixes #13980. Closes gh-214.