repaired regular expression

It was pointed out to me that the regular expression had a slight error: It would incorrectly match prefixes, meaning that if I had a tag `<codetest>`, because it starts with `code`, it would get matched.

Instead, use a non-capturing group to force a whitespace first, because we want to match things of the form `<code test...>` not `<codetest>`

The submitted regular expressions fix this.