[lmi] A wx style question

[Greg Chicares]

The wx manual specifies these default arguments:

wxTreeItemId AppendItem
    (const wxTreeItemId& parent,
    const wxString& text,
    int image = -1,
    int selImage = -1,
    wxTreeItemData* data = NULL)

When we need to specify all five arguments, but want defaults
for the third and fourth, should we write them as '-1'? Or is
there some constant (like 'wxDefaultSize' for wxSize arguments)
that's preferable?