- Rich sentences (a link or button inside text) can be replaced by data: the inventory gives a rich entry `slots`, a pack value places the site's own elements with {e0}, {e1}, ... (each once, the last may be left out; no markup, plural or other parameters). The engine returns a pieces + element order template; the page inventory carries `rich` slot counts.
- Packs may carry `when: { languages }` (applies only while the site shows one of them; `en` matches `en-GB`) and `rewrite: { words }` (whole-word rewording of the site's own text, messages keep their parameters' values; no sentences of the site in the pack). The hook tells the engine the site's language; a rewording pack makes the delivery carry the whole inventory.
- Apps can ship built-in packs (BuiltInPacks) delivered before installed ones; syncStringPacks hands the tabs a delivery at start only when it changed.
- Translate mode words are a function the app supplies (asked at each draw) and gain a `plural` word; host validates `when` and `rewrite` envelopes.
- Theme doctor: every finding says where (token path or CSS rule), what and how to fix, as catalog keys wb.doctor.*; the Theme Builder shows the full report; the import hint is translated. Doctor words are in the 17 supported catalogs.
- waybetter strings check describes conditions and rewrites.
