PanelSize
PanelSize =
"small"|"medium"|"large"|"none"
Defined in: components/panels.ts:103
How wide a panel asks to be — a ceiling the shell never exceeds; see
Panel.maxWidth. "small" is the column the content area is divided
into; "medium" and "large" are two and three of those, and "none" is
the whole area. Each is capped at the content area, so on a narrow window
they all come to the same thing.