Removal of rules in ABNF grammars.
It is sometimes useful to remove from a grammar
all the rules that define certain rule names.
For example, the SMTP grammar specified in RFC 5321 references rules defined in the IMF grammar specified in RFC 5322. The IMF rules depend on a rule atom,
but the SMTP rules provide their own definition of Atom
(recall that rule names are case-insensitive).
Thus, before plugging the IMF rules into the SMTP rules,
the removal operation can be used to remove, from the IMF rules,
atom and possibly any other rule already defined by SMTP.
- Remove from a list of rules all the ones
that define one of the given rule names.