diff --git a/docs/swarm/ui.md b/docs/swarm/ui.md
index 11ce8fd6..d050ad8b 100644
--- a/docs/swarm/ui.md
+++ b/docs/swarm/ui.md
@@ -20,6 +20,9 @@ the highlighted one. **Escape**, **Tab** or a press elsewhere shut the list with
 changing anything. Typing the start of an option's name picks it, also with the list
 shut. A dropdown inside a dialog opens above the dialog and the dialog doesn't cut it off.
 
+A dialog grows to fit its content, up to 64em or nine tenths of the window, whichever is
+smaller; short confirm dialogs stay short.
+
 | route                                          | what                                                                                                                                                                                                                                                                                                                                                                                            |
 | ---------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
 | `/`                                            | the start page: the swarm's name over a digital-rain backdrop with the slug (`hyperhive / we are the wired`, its shaded gradients pulsing in a wave unless reduced motion is on) at the foot, plus a paperclip offering to set up an agent while no `ruth` exists, or her hive declares her destroyed (it opens the create form with `ruth` filled in); the swarm name in the header links here |