We always advise to write documented code. So why should we ignore this when writing regexes? There are several techniques to document your regex. Using eXtended mode is the recommended way. I took the regex from this StackOverflow answer to demonstrate this method.
This is the preferred and most common way of implementing comments by using the x modifier:
// Regex for password validation
$regex = '/
^ # start-of-string
(?=.*[0-9]) # a digit must occur at least once
(?=.*[a-z]) # a lower case letter must occur at least once
(?=.*[A-Z]) # an upper case letter must occur at least once
(?=.*[@#$%^&+=]) # a special character must occur at least once
(?=\S+$) # no whitespace allowed in the entire string
.{8,} # anything, at least eight places though
$ # end-of-string
/x';Basically spaces are ignored, everything after a hashtag will get ignored as well. Here comes the pitfall: since spaces are ignored, what if I want to match a space? There are several ways, I will show two of them. Say I want to match one or more spaces:
- Escaping the space
$regex = '/\ +/x'; - Using a character class:
$regex = '/[ ]+/x'
That said, regardless of the x modifier, I would always enclose the space in a character class. It's clear that way.