Character Class[a-f\d\-]+ +matches at least one character from the set below:
a-fone character from a (9710) to f (10210) (case sensitive)
\da digit
\-the literal - (4510 / 558 / 2D16)
Comment: Matches a-f, any digit, - (hyphen)
Comment: ^ One or more times (+)
\/the literal / (4710 / 578 / 2F16)
Comment: Matches a /
.+any character (except for line terminators), repeated at least once
Comment: Matches any character one or more times
\.the literal . (4610 / 568 / 2E16)
Comment: Matches a . (dot)
(?i)applies the following effective flags to the remainder of the pattern: xi i modifier: insensitive. Matches without distinguishing uppercase and lowercase letters
Comment: States that anything after this is case-insesitive
Comment: ^ Inline Flag
Group 1(jpg|jpeg|gif|png) jpgthe literal text jpg (case insensitive) jpegthe literal text jpeg (case insensitive) gifthe literal text gif (case insensitive) pngthe literal text png (case insensitive) Comment: Selects file extension
Comment: ^ (either jpg, jpeg, gif, or png)
(?-i)applies the following effective flags to the remainder of the pattern: x i modifier: -insensitive. Case-sensitive match
Comment: Removes Inline Flag
x modifier: extended. Ignores unescaped whitespace and comments outside character classes