The state represented by TCHT_ONITEM Win API flag is not a superposition
TCHT_ONITEMICON and TCHT_ONITLABEL states but it represents a separate state.
The fact that binary value of TCHT_ONITEM is bitwise-OR operation on
TCHT_ONITEMICON and TCHT_ONITEMLABEL doesn't matter here. The same applies to
wxBK_HITTEST_xxx flags where state represented by wxBK_HITTEST_ONITEM is not a
superposition of wxBK_HITTEST_ONICON and wxBK_HITTEST_ONLABEL.
Add note to wxBookCtrl::HitTest documentation that wxBK_HITTEST_ONICON,
wxBK_HITTEST_ONLABEL, wxBK_HITTEST_ONITEM are mutually exclusive bits.
See https://github.com/wxWidgets/wxWidgets/pull/159
1237e932ad