Document regex adverb :dba

[tisonkun]

BTW, what :dba is?

> 'abc' ~~ /:dba('foo') abc/
Nil

confusing

[tisonkun]

[20:07] <moritz> (dba stands for "do business as", and is supposed to set the current rule name for use in error messages)
[20:09] <jnthn> I'm not totally sure we ever implemented :dba in Rakudo
[20:10] <jnthn> It's certainly in NQP, 'cus we use it for a load of error reporting :)

So maybe it has nothing to do with rakudo or perl6 spec. I'll remain the issue until we reach an agreement.

[AlexDaniel]

I think dba was actually implemented in some of TimToady's reverted commits for the change that made Grammar.parse return a useful error message rather than just Nil. Or maybe these particular commits were not reverted even.

[tisonkun]

internal feature maybe, not customer-facing