Allows the contents of individual cells in the column to be changed, especially useful when <treecol type="checkbox">. Also useful for disabling editing of individual treecells. When the user double-clicks an editable cell, a text field appears in which the user can edit the contents of the cell.
The tree and treecol must also be marked as editable in order for this to work. The tree must be a content tree for this to work on treecells.