message: docs(compiler): add comment to warn about regexp changes
  ref
diff: @@ -12,6 +12,7 @@ const _SELECTOR_REGEXP = new RegExp(
  '(\\:not\\()|' + //":not("
  '([-\\w]+)|' + // "tag"
  '(?:\\.([-\\w]+))|' + // ".class"
  + // "-" should appear first in the regexp below as FF31 parses "[.-\w]" as a range
  '(?:\\[([-.\\w*]+)(?:=([^\\]]*))?\\])|' + // "[name]", "[name=value]"
  '(\\))|' + // ")"
  '(\\s*,\\s*)', // ","
  