Here is the specification for a Menu structure:

    struct Menu
        {
        struct Menu *NextMenu;
        WORD LeftEdge, TopEdge;
        WORD Width, Height;
        UWORD Flags;
        BYTE *MenuName;
        struct MenuItem *FirstItem;
        WORD JazzX, JazzY, BeatX, BeatY;
        };

The variables in the Menu structure have the following meanings:

NextMenu
    This variable points to the next Menu header in the list.  The last
    Menu in the list should have a NextMenu value of NULL.

LeftEdge, TopEdge, Width, Height
    These fields describe the select box of the header.  Currently, any
    values supplied for TopEdge and Height are ignored by Intuition,
    which uses instead the top of the screen for the TopEdge and the
    height of the screen's title bar for the Height.

    LeftEdge is relative to the LeftEdge of the screen plus the screen's
    left border width, so if LeftEdge is 0, Intuition puts this header at
    the leftmost allowable position.

Flags
    The flag space is shared by the program and Intuition.  The flags are:

    MENUENABLED
        This flag is for Intuition's use and indicates whether or not
        this Menu is currently enabled.  Set this flag before submitting
        the menu strip to Intuition.  If this flag is not set, the menu
        header and all menu items below it will be disabled, and the
        user will be able to view, but not select any of the items.
        After submitting the strip to Intuition, the disabled or enabled
        status may be changed by calling OnMenu() or OffMenu().

    MIDRAWN
        This flag indicates whether or not this menu's items are
        currently displayed to the user.

MenuName
    This is a pointer to a NULL terminated character string that is
    printed on the screen's title bar starting at the LeftEdge of this
    menu's select box and at the TopEdge just below the screen title
    bar's top border.  The text is rendered in the screen's font.

FirstItem
    This points to the first MenuItem structure in the linked list of
    this menu's items.

JazzX, JazzY, BeatX, BeatY
    For internal use only.