Function menu_panel_spec 

pub fn menu_panel_spec(t: &Theme, m: &Metrics) -> NodeSpec

The panel every menu is: a fixed-width column of rows, in the palette the stock menu paints. What the caller adds is where it goes and what scope it belongs to — a context menu floats at the pointer and declares its own modal; the menu bar’s drops out of its title and lives inside the bar’s. Takes the palette and the metrics rather than reading them, because a caller that has a Ui in one hand cannot lend it to this and to menu_panel in the same expression; let t = ui.theme(); first is the idiom.