ReadonlyChangesReadonlySectionsA section arrived on or left the page after the rail was worked out. A panel that draws its section only once its data has loaded (the Feature Values and Model Predictions panels, for instance) mounts inside a slot after every structural trigger the container watches has fired; without this the section belongs to no rail group, and on a left-nav form that means it never shows.
Accordion hides every More member — field panels included — until the overflow footer is expanded. Left-nav does not use this.
Per-container chrome state. Provided by
<mj-record-form-container>so projected panels and fill-in stock grids share one spec.