Question 1

Why doesn't a slow pattern freeze the page?

Accepted Answer

The pattern runs in a separate thread and is stopped if it doesn't finish within two seconds. So catastrophic-backtracking expressions like (a+)+ won't lock your tab — but remember the same expression will stall your server.

Question 2

How do I write a named group?

Accepted Answer

As (?<name>...). The tool lists named groups in their own column; in code you read them via match.groups.name, which won't break when the order changes.

Regex Tester