CellCallback 
    The type of the callback functions used for iterating over the cell renderers of a GtkCellArea, see gtk_cell_area_foreach().
- param - rendererthe cell renderer to operate on
- return true to stop iterating over cells. 
The type of the callback functions used for iterating over the cell renderers of a GtkCellArea, see gtk_cell_area_foreach().
param renderer the cell renderer to operate on
return true to stop iterating over cells.