True when this scope is open/active and its contents may be submitted. Call EndTooltip() only when true; on false, skip both contents and the matching end.
Tooltips are windows following the mouse. They do not take focus away.
A tooltip window can contain items of any types.
SetTooltip() is more or less a shortcut for the 'if (BeginTooltip()) { Text(...); EndTooltip(); }' idiom (with a subtlety that it discard any previously submitted tooltip)
begin/append a tooltip window.
Begin a tooltip window.