Sub-menus
Menus are sometimes hierarchically organized, allowing navigation through different levels of the menu structure. Selecting a menu entry with an arrow will expand it, showing a second menu (the sub-menu) with options related to the selected entry.
Usability of sub-menus has been criticized as difficult, because of the narrow height that must be crossed by the pointer. The steering law predicts that this movement will be slow, and any error in touching the boundaries of the parent menu entry will hide the sub-menu. Some techniques proposed to alleviate these errors are keeping the sub-menu open while moving the pointer in diagonal, and using Mega Drop-Down menus designed to enhance scannability and categorization of its contents.
Read more about this topic: Menu (computing)