[0-9]       : one character, value 0-9 ([1-35-6] : a character that is either 1 or 2 or 3 or 5 or 6)
[0-9][a,b]  : two characters, combination of both (0a or 0b or 1a or 1b or 2a ... 9a or 9b)
[0-9][0-9]? : one or two characters; character infront of "?" is optional
a{1,3}h     : character infront of {} can be repeated by the number inside of {} (ah, aah, aaah)
[0-9]{5}    : looks for a five-digit number (00000 to 99999)
[0-9]{3,}   : at least three-digits (000 to 999 or 0000 to 9999 ...)
.           : any character (a.c : aac or abc or acc or adc ...)
\           : masking character
[^x]        : any character except x
(ab)        : groups a and b, looks for ...ab...
|           : or (a|b : a or b)