split("aaa??aaa"",$mystring) where "?" may be any character. How?

[JoeZar]

I have a long string I want to split into fragments. To delimite the fragments I want to use a sequence (p.e. "aaa??aaa") from which I know some character, but others are unkwon (so that I want to split the string when it contains "aaabbaaa", "aaaccaaa","aaaddaaa", etc.) . The number of unkwon characters will be allways kwon.

[Plakhotnik]

You can use preg_relpace.