Build, test, and debug regular expressions
Matches MediaWiki-style internal wikilinks such as [[Page]], [[Page#Section]], or [[Page|Display Text]]. Capture group 1 holds the page title, while the optional pipe alias (display text) is captured in group 2; the section anchor after # is matched but not captured. Useful for parsing wikitext, extracting links from Wikipedia dumps, or converting wikilinks to Markdown/HTML.