Convert raw HTML into clean GitHub-Flavored Markdown: ATX headings, fenced code, pipe tables, strikethrough, task lists; script/style/iframe text is always stripped. mode=article isolates the main article with Mozilla Readability (returns title, byline, excerpt; drops nav/footer boilerplate; resolves relative links), else converts the whole document. Converts provided HTML only — never fetches URLs. Max 5 MB.