Re: New keybinding suggestion: C-x _ for `shrink-window'

[Richard Stallman]

      By default, resizing is done by increasing/decreasing window
      width and height.  In this mode, use the up and down arrow keys
      to enlarge or shrink the window and use the right and left arrow
      keys to enlarge or shrink the window horizontally.

So in this mode you don't control which border moves.

      Resizing can also be done by moving the window borders.  In this
      mode, use the arrow keys to move the corresponding border in the
      arrow direction -- e.g. the left arrow key will try to move the
      left border to the left.

So in this mode you can only enlarge the window.

    When the point is in window B and you're in move-borders mode, <left>
    will move the left border of window B to the left, and <right> will move
    its right border to the right.  But you might want to quickly move the
    left border to the right.  So instead of finding window A and moving its
    right border to the right, you'll negate the argument and move the left
    border (which will move to the right instead of moving to the left.)

Oh, so that's how you would use the window borders mode to make this
window smaller.

It seems unnatural, and I think it will be hard to remember.

Perhaps the right thing to do is use arrow keys to select the border
to move, and use + and - to grow or shrink the window using that border.