Regex: Matching against groups in different order without repeating the group

Question

Let\'s say I have two strings like this:

XABY
XBAY

A simple regex that matches both would go like this:

X(AB|BA)Y

Answer 1

If there are several strings, with any kind of characters in there, you'll be better with:

X(.)+Y

Only numbers then

X([0-9])+Y

Only letters

X([a-zA-Z])+Y

Letters and numbers

X([a-zA-Z][0-9])+Y