SPLITCHILD_WND | the child pane is an ordinary window. In this case the following
members must be used: class, text, style, id. pCtlData and pPresParams are optional. |
SPLITCHILD_DLG | the child pane is a dialog window. In this case the following
members must be used: pDlgProc, hmod, id, type. pCtlData is optional. |
SPLITCHILD_SPLIT | the child pane is a nested splitpane. The mandatory members in this case are: style, id, pSplitCreate and type. |