Suppose the string library had a function `string.defineclass`.
string.defineclass("%u",utf8.charpatt)
stdin:1: attempt to redefine a built-in character class
string.defineclass("%Z",utf8.charpatt)
stdin:1: bad argument #1 to 'defineclass' (must be lowercase)
string.defineclass("%z",utf8.charpatt) -- then do some great stuff with %z and %Z
string.defineclass("%z",nil) -- %z and %Z not available anymore
What could be allowed as second argument (string, table, function?)
will come out during implementation.
If the proposed "text" mode could be implemented on top of
that, we will have gained a lot more.
