4 * Fix `is_whitespace`, add more tests
5 * Add more thorough tests for idents for XID_Start & XID_Continue
6 * Validate that float and integer literals use digits only of the appropriate
8 * Validation for unclosed char literal
9 * Strings are completely wrong: more tests and comparison with libsyntax.
10 * Comment lexing is completely wrong
13 * Figure out what is the expected state of attribute grammar.
14 Token trees or something more structured? Token trees would be unfortunate: no extend selection =/