The form factor of the surface your app is rendered into, mirrored from the
immediately.run host (UI_AS_APPS_SPEC §5.4.1). Read this to lay out
responsively — a narrow chrome panel, a full preview, or a mobile carousel
pane all report their box here. The host is the source of truth (it owns the
region); you cannot reliably measure your own viewport across the sandbox
boundary.
Baseline capability formFactor:read — every app may read it.
The form factor of the surface your app is rendered into, mirrored from the immediately.run host (UI_AS_APPS_SPEC §5.4.1). Read this to lay out responsively — a narrow chrome panel, a full preview, or a mobile carousel pane all report their box here. The host is the source of truth (it owns the region); you cannot reliably measure your own viewport across the sandbox boundary.
Baseline capability
formFactor:read— every app may read it.