Extraction: HTML is not text
A raw crawled page is HTML: navigation bars, ad slots, cookie banners, comment sections, and — somewhere in there — the actual content. Boilerplate extraction tools (trafilatura, jusText, and similar) try to isolate the main readable content, and the extractor chosen measurably changes downstream corpus quality: an aggressive extractor strips useful context along with the boilerplate, while a lax one leaves navigation menus and cookie notices as 'training data'.