ize of the selection.
        const selectionStartBound = computeCharacterBound(selectionStart);
        const selectionEndBound = computeCharacterBound(selectionEnd);
        editContext.updateSelectionBounds(DOMRect.fromRect({
          x: selectionStartBound.x,
          y: selectionStartBound.y,
          width: selectionEndBound.x + selectionEndBound.width - selectionStartBound.x,
          height: selectionStartBound.height
        }));
      }

      // Update the EditContext's control bounds.
      