Constant URL_WWW_STR 

pub const URL_WWW_STR: &str = "www\\.(?:[a-zA-Z0-9][-a-zA-Z0-9]*\\.)+[a-zA-Z]{2,}(?:/[^\\s<>\\[\\]\\\\\'\\\"`]*)?";

Pattern for www URLs without protocol.

Matches URLs starting with www. that lack a protocol prefix. These should be converted to proper URLs or flagged as bare URLs.