Begins editing on a this.
The CellRenderer for the cell creates and returns a CellEditable from start_editing, configured for the CellRenderer type.
start_editing can then set up this suitably for editing a cell, e.g. making the Esc key emit editing_done.
Note that the this is created on-demand for the current edit; its lifetime is temporary and does not persist across other edits and/or cells.
| this | |
| event |
The Event that began the editing process, or null if editing was initiated programmatically |