function IsControlMouseMsg(var Message: TWMMouse): Boolean;
bool __fastcall IsControlMouseMsg(Winapi::Messages::TWMMouse &Message);
Indicates whether a specified mouse message is directed to one of the windowed control's child controls.
Call IsControlMouseMsg to find out if a mouse message is directed to one of the control's child controls. Specify the mouse message as the value of the Message parameter.
Windows takes care of sending messages to windowed child controls, but for nonwindowed child controls, Windows sends the messages to the parent control, which must then determine which, if any, of its child controls should receive the message.