mhalabi-google

@MichaelRybak Thank you for the review. Please take another look.

> @alanorozco The validator error seems redundant ("ValidatorRulesMakeSense : value_regex_casei must have unicode named groups"). The expression (tracking ID) should only support English letters. What do you suggest to fix...

> @mhalabi-google I'd suggest using [A-Z0-9] instead of \w. > > The test ensures that every \w is followed by \p{L}\p{N}. Although excessive, it prevents developer from forgetting to support...

> @alanorozco Tests are passing now. Thank you for the help!

@alanorozco Can you please merge this to head?