Scrolls list horizontaly. This supposes that the list is packed into a scrolled window or something similar, and adjustments are well set. Step and page increment are those from the horizontal adjustment of list . Backward means to the left, and forward to the right. Out of bounds values are truncated.
Scrolls list vertically.
This supposes that the list is packed into a scrolled window or something similar, and adjustments are well set. Step and page increment are those from the vertical adjustment of list . Backward means up, and forward down. Out of bounds values are truncated. Toggles between adding to the selection and beginning a new selection.