Wx::CheckBox is missing methods for three-state operation.  The documentation lists 3-state methods (#get_3_state_value,
#is_3_rd_state_allowed_for_user, #is_3_state, #set_3_state_value) which do not exist in an actual instance of the CheckBox
class.

The style constants are also missing:  Wx::CHK_2STATE, Wx::CHK_3STATE, and Wx::CHK_ALLOW_3RD_STATE_FOR_USER.  

NOTE:  Passing the correct integer value for CHK_3STATE (4096) as the style does not make the 3-state methods appear.