labelWidget label; interactive widgets also use it for ID generation. A ## suffix can distinguish IDs without displaying the suffix.
preview_valueText displayed in the closed combo preview; null leaves the preview empty.
flagsImGuiComboFlags options controlling this operation; combine compatible flag bits with |.
True when this scope is open/active and its contents may be submitted. Call EndCombo() only when true; on false, skip both contents and the matching end.
The BeginCombo()/EndCombo() api allows you to manage your contents and selection state however you want it, by creating e.g. Selectable() items.
The old Combo() api are helpers over BeginCombo()/EndCombo() which are kept available for convenience purpose. This is analogous to how ListBox are created.
Begin a combo-box popup for custom items.