AMIGA FONTS
        The existence of a disk font is indicated by the existence of
        its associated font contents file, whose name has the suffix
        ".font".  It is this name that is used in the actual font
        open call of the application.  Amiga fonts are collected in
        the directory path(s) associated with the FONTS: assign.  It
        is this assign that is searched if no explicit path name is
        provided in the font open call: use of an explicit path is
        generally discouraged.  The actual bitmaps of traditional
        Amiga fonts are stored in a directory with the name of the
        font contents file stripped of its ".font" suffix.  This
        directory is usually in the same directory as the font
        contents file.  This traditional arrangement is supported by
        the FixFonts system application.

        For example:
            o   FONTS: is assigned to Sys:Fonts/
            o   Sys:Fonts/garnet.font exists and describes that the
                font "garnet.font" exists
            o   Sys:Fonts/garnet/ contains the bitmap images for
                sizes 9 and 16

        Other variations of file placement may exist, but they
        require custom tools to maintain -- tools available not from
        Commodore, but from other sources such as Fish disks.

        Font contents files are flagged with magic numbers that not
        only verify that they are a font contents files but also what
        variation of file structure they contain.

   OUTLINE TYPEFACES
        The existence of an outline typeface is indicated by a magic
        number in the font contents file.  They are further described
        in the associated outline typeface tag file, whose name is
        the that of the font contents file with the suffix ".otag"
        substituted for ".font".  This tag file contains a tag list
        that is to be processed and passed to the outline engine
        (i.e.  bullet.library) in order to select the associated
        typeface.  It also contains information applications may use
        to guide their use of the typeface.

   OTAG SPECIFICATION EXAMPLE
        Here are the steps necessary to go from an arbitrary font
        name into an environment where glyphs from that font
        can be accessed:
        1.  read the header from the font contents (.font) file and
            verify that the magic cookie fch_ID is OFCH_ID.
            If it is not, then this is an Amiga bitmap font,
            not an outline font.
        2.  read the associated outline tag (.otag) file into memory:
            a.  Validate that the OT_FileIdent exists and matches the
                file size.
            b.  allocate a memory buffer and read the file into it.
            c.  Resolve addresses: for each tag with the OT_Indirect
                bit set, add the memory buffer origin to the
                associated data.
        3.  Find the OT_Engine tag and ensure that you have the
            proper engine open:
            a.  If you already have an engine handle for this engine
                name, you skip these steps.
            b.  append the suffix ".library" to the engine name.
                (e.g. "bullet" becomes "bullet.library").
            c.  use exec's openlibrary() to open the library.
            d.  use the engine's openengine() to acquire an engine
                handle.
        4.  Pass the full path name of the .otag file to the engine
            with the OT_OTagPath tag using SetInfo().
        5.  Pass the memory copy of the .otag file to the engine with
            the OT_OTagList tag using SetInfo().  This step may be
            combined with step 4, passing first the path then the
            list in one call.
        The library is now ready to accept glyph metric information
        (e.g. size and glyph code) and produce glyph bitmaps.

   DISKFONT USE OF OTAG ENTRIES
        The diskfont library uses other entries from the outline tag
        (.otag) file.  The following are used both during inquiry of
        what typefaces exist (AvailFonts) and during creation of an
        Amiga textfont (opendiskfont):
        o   OT_IsFixed is used to determine whether these outlines
            describe a PROPORTIONAL flagged font.
        o   OT_StemWeight is used to determine whether these outlines
            describe a BOLD style font.
        o   OT_SlantStyle is used to determine whether these outlines
            describe an ITALIC style font.
        o   OT_HorizStyle is used to determine whether these outlines
            describe an EXTENDED style font.
        The following are used only during OpenDiskFont:
        o   OT_YSizeFactor is used to convert the Amiga pixel height
            specification, which describes the distance from the
            lowest decender to the highest ascender, into a point
            size specification, which is related (via YSizeFactor)
            to a nominal character height.
        o   OT_SpaceWidth is used as the width of the space character.
        The following is used only during AvailFonts:
        o   OT_AvailSizes is used to generate a list of sizes
            available for the font.