Alpha. The app sub-resource may change shape without a deprecation cycle while apps mature. The document routes are stable.

Apply targeted edits to the app on an existing draft without resending the HTML body: any subset of htmlEdits (exact-substring search/replace operations, applied in order) and settings (full replacement). All-or-nothing — an edit that matches zero times, matches more than once without replaceAll, or would push the HTML past the 2 MiB cap rejects the whole request with 400 naming the edit, and nothing is applied.

Content addressing buys sequential staleness detection, not concurrency safety: if the text an edit targets moved between your read and your write, the edit fails to match and nothing is applied. There is no version precondition, compare-and-swap, or lock behind it, so two writers patching the same app at the same time can still overwrite each other, orthogonal edits included — serialize writes to one app when that matters. PATCH never creates the app: a draft with no app is a 409 (create it with PUT).

A document carries at most one of a dashboard or an app — never both; workbook-only is valid. The app HTML and settings live only at the app sub-resource routes; the document read carries an app slice pointing here, and the whole-document PATCH accepts that slice back only as it was read.