A data type used for identifying handlers without tedious string comparisons.
typedef uint32_t LEOHandlerID;
Every handler name maps to a handler ID. Since handler names are case-insisensitive, "mouseUp", "MOUSEUP" and "mouseup" would all map to the same handler ID. Not unlike a "selector" in Objective C.
#define kLEOHandlerIDINVALID UINT32_MAX
Indicate that a handler ID variable has not been set yet.