Returns the mark that represents the selection bound. Equivalent to calling TextBuffer.getMark to get the mark named “selection_bound”, but very slightly more efficient, and involves less typing.
The currently-selected text in buffer is the region between the “selection_bound” and “insert” marks. If “selection_bound” and “insert” are in the same place, then there is no current selection. TextBuffer.getSelectionBounds is another convenient function for handling the selection, if you just want to know whether there’s a selection and what its bounds are.