ReadonlySectionThe chrome section key this source reports for (matches mj-collapsible-panel SectionKey).
Current state. Called during change detection — must be cheap and side-effect free.
Whether a form-level ValidationErrorInfo belongs to this section. Used only to
decide which errors are UNROUTED (claimed by no section), so a failure nothing
renders still reaches the form-wide total instead of vanishing.
Anything that can answer "what is the state of section X right now".
mj-collapsible-panelimplements this for every section it renders, deriving the counts from itsmj-form-fieldchildren. A custom section that is NOT a collapsible panel — a hero, a designer, a grid editor — can implement it too and register with the container's FormSectionIndicatorCoordinator, so the rail treats it like any other section.