regex - Regular Expressions for sequences other than strings -

do there exist regular expression engines sequences other strings? occurs me there nothing special strings restricts regex them, sequences of characters.

for example, if had list of buffalo objects, , wanted check if list matched between 4 , 7 buffalo on 5 ft tall, followed white buffalo, followed backreference 4-7 buffalo before, , end of list, there engines support this?

i don't have need this, curious.

regular expressions work on strings, not objects. if want match object keys or values going have iterate on them.