See samples.

XTWM_PROPERTYGRID_NOTIFY +

const UINT XTP_PGN_SORTORDER_CHANGED  = 1; // The sort order has changed in the property grid.
const UINT XTP_PGN_SELECTION_CHANGED  = 2; // The selection has changed in the property grid.
const UINT XTP_PGN_ITEMVALUE_CHANGED  = 3; // The value has changed for pItem in the property grid.
const UINT XTP_PGN_EDIT_CHANGED      = 4; // The edit value has changed in the property grid.
const UINT XTP_PGN_INPLACEBUTTONDOWN = 5; // Item's inplace button (combo or expand) down.
const UINT XTP_PGN_DRAWITEM = 6;   // Item's draw event.
const UINT XTP_PGS_OWNERDRAW = 0x0010L;  // Apply this style to the property grid to use the owner draw feature.

const UINT XTP_PGN_ITEMEXPANDCHANGED = 7; // Item's inplace button (combo or expand) down.

const UINT XTP_PGN_DBLCLICK = 8;         &nbs p;  // Double click event.
const UINT XTP_PGN_RCLICK = 9;