Return a comparison's redline once it is ready.

Returns the comparison POST /v1/compare started, by comparison_id, its redline as file in each format asked for: docx (Word tracked changes, the default), pdf, pdf_changed_pages_only, md (its listing: the text with the changes marked), json, or html; a PowerPoint comparison offers pptx and pdf, an Excel comparison xlsx. To show the user the redline, ask for pdf; ask for docx only when the user's own words name Word, .docx or tracked changes, or after they have seen the PDF and ask for it. A document's type alone is not a reason to. A person sees the PDF, or the html redline where the view must be interactive; md is for a model to read, and json for code to act on, never to draw the redline from. While formats are pending, status is processing: call again with the same arguments until it is ready. Status failed is terminal for the formats in file.failed_formats, or for the whole comparison when error is present. Each file.downloads[] entry's url serves the file directly; the links expire after one hour.

"Compare," "redline" or "diff" by themselves mean produce the file, not explain it.

When the user asks what changed, to explain, summarize or answer a question about the changes, read the redline's listing: the file.downloads[] entry of format md (ask for format=md), or GET /v1/files/{file_id}?format=md by file.file_id to search it. Its <ins>, <del>, <moved-from> and <moved-to> elements are the exact tracked-change set, each naming its revision, and the <revision/> lines at its end list every revision with its type, author and date; its header says what each tag means.