This virtual method should be implemented to navigate focus from
cell to cell inside the gtk.cell_area.CellArea. The gtk.cell_area.CellArea should move
focus from cell to cell inside the area and return false if focus
logically leaves the area with the following exceptions: When the
area contains no activatable cells, the entire area receives focus.
Focus should not be given to cells that are actually “focus siblings”
of other sibling cells (see gtk.cell_area.CellArea.getFocusFromSibling).
Focus is set by calling gtk.cell_area.CellArea.setFocusCell.
This virtual method should be implemented to navigate focus from cell to cell inside the gtk.cell_area.CellArea. The gtk.cell_area.CellArea should move focus from cell to cell inside the area and return false if focus logically leaves the area with the following exceptions: When the area contains no activatable cells, the entire area receives focus. Focus should not be given to cells that are actually “focus siblings” of other sibling cells (see gtk.cell_area.CellArea.getFocusFromSibling). Focus is set by calling gtk.cell_area.CellArea.setFocusCell.