Basically, you are matching filenames that start with a letter
or digit
, followed by the characters letter
, digit
, -
, .
, _
, any number of times up to 27, even 0 times. Then, there is a .
, probably separating the extension, which is composed of a letter
followed by the characters letter
, digit
any number of times from 1 to 3.
Some examples:
a.aa
,
0_.A0a
,
A---____-_.a999