Challenges

Capture the major, minor and patch numbers of a version, plus its prerelease tag — or nothing in group 4 when there is no prerelease.

Match strings containing "cat" or "dog" as a whole word.

A noughts and crosses board arrives as one flat string. Match it only when X has three in a row — across, down, or diagonally.

Match a valid CSS hex colour — a # followed by exactly three or six hex digits, and nothing else.

Rewrite a log line "DATE TIME LEVEL MESSAGE" as "[LEVEL] MESSAGE (TIME on DATE)".

A white pawn checks the black king from the square down-left or down-right of it. Capture both squares.

Capture the year, month and day of an ISO date as three separate groups.

Capture the key and the value from a "key = value" line, whatever the spacing.

Pull the timestamp, the level and the message out of a bracketed log line.

Turn "Ada Lovelace" into "Lovelace, Ada".

Capture the text inside the FIRST <b>...</b> tag on the line — just the text, not the tags.

Rewrite every DD/MM/YYYY date as YYYY-MM-DD, leaving the rest of the text alone.

Capture everything before the FIRST equals sign: key=value=other gives key.

Capture the file extension of a filename: report.q3.pdf gives pdf, not q3.pdf.