+ * This is used by the outside_in/drupal.off_canvas library to select the
+ * "main canvas" page element as opposed to the "off canvas" which is the tray
+ * itself. The "main canvas" element must be resized according to the width of
+ * the "off canvas" tray so that no portion of the "main canvas" is obstructed
+ * by the tray. The tray can vary in width when opened and can be resized by the
+ * user. The "data-off-canvas-main-canvas" attribute cannot be removed without
+ * breaking the off-canvas dialog functionality.