2) Your regression test for the modernTab clef:
Doc header should say "four- to seven- stringed instruments", which means
instruments having four to seven strings. "four to seven stringed
instruments" means four to seven instruments having strings. Isn't english
fun?
You should demonstrate in the regtest that it works for four strings and
seven strings, and that it works with various staff sizes. You may want two
different regtests -- one that shows variations in string numbers and one
that shows variation in sizes.