It validates an email address with alias

Find PHP object variables, and replace them with (array)brackets.

with Leap Year support (dd/MM/yyyy)

match with or without prevailing/trailing slashes

get special tag contains html link

Remove multiple white spaces between words and replace it with the char of your choosing.

Extract parts of an URL.

RegEx for an .htaccess rewrite into a subfolder without provoking a 'too many redirects' error

1 Uppercase 1 lower case 1 number 1 not a number or letter

^((?!proposed_).)*((project|task)_details) matches: project_details task_details...

It's too large to match with all which seems like an IPv6. It's not perfect, but it's detects more valid IPv6 than some others regex.

This expression matches human genomic coordinates, similat to those being used by genome browsers (e.g. the UCSC Genome Browser). It can match: chromosome, chromosome start, chromosome start end, chromosome start end reference sequence, chromosome start end reference sequence alternative sequence. T...

This expression escapes characters, which have a special meaning in regex, like .?[]/ and so on. Use it to transform a string that you want to use literally in another regex.