???? → 4 chars

* → any number of chars

[:upper:] ⇔ [A-Z] same for [:lower:] and [:digit:]

[:alpha:] ⇔ [a-zA-Z]

[:alnum:] ⇔ [a-zA-Z0-9]

ls -l [a-d] → part of a range

^ and $ works like in regex

la a*.{doc,docx} → OR

ls a*.(doc|docx) → OR