See external documentation: wxSplitterEvent.

Use wxEvtHandler:connect/3 with EventType:

command_splitter_sash_pos_changed, command_splitter_sash_pos_changing, command_splitter_doubleclicked, command_splitter_unsplit

See also the message variant #wxSplitter{} event record type.

This class is derived (and can use functions) from:
wxNotifyEvent
wxCommandEvent
wxEvent