NAME
        MapTags -- convert ti_Tag values in a list via map pairing. (V36)

   SYNOPSIS
        MapTags(tagList,mapList,mapType);
                A0      A1      D0

        VOID MapTags(struct tagitem *,struct tagitem *,ulong);

   FUNCTION
        Apply a "mapping list" mapList to tagList.

        If the ti_Tag field of an item in tagList appears as ti_Tag in some
        item in mapList, overwrite ti_Tag with the corresponding ti_Data
        from the map list.

        The mapType parameter specifies how the mapping operation is to
        proceed, with the following available types:

                MAP_REMOVE_NOT_FOUND
                If a tag in tagList does not appear in the mapList, remove
                it from tagList.

                MAP_KEEP_NOT_FOUND
                To have items which do not appear in the mapList survive the
                mapping process as-is.

        MapTags() is central to BOOPSI gadget interconnections where you want
        to convert the tag values from one space (the sender) to another (the
        receiver).

        The procedure will change the values of the input tag list
        tagList (but not mapList).

        You can "filter" a list by passing MAP_REMOVE_NOT_FOUND as mapType,
        and having the data items in mapList equal the corresponding tags.

        You can perform the inverse filter ("everything but") by passing
        a mapType of MAP_KEEP_NOT_FOUND, and creating a map item for every tag
        you want to filter out, pairing it with a mapped data value of
        TAG_IGNORE.

        For safety and "order independence" of tag item arrays, if you
        attempt to map some tag to the value TAG_DONE, the value TAG_IGNORE
        will be substituted instead.

   INPUTS
        tagList - input list of tag items which is to be mapped to tag values
                  as specified in mapList.
        mapList - a "mapping list" tag list which pairs tag values expected to
                  appear in tagList with new values to be substituted in the
                  ti_Tag fields of tagList (may be NULL)
        mapType - one of the available mapping types as defined in
                  <utility/tagitem.h>

   EXAMPLE
        /* Consider this source list: */
            struct tagitem list[] =
            {
                {MY_SIZE,       71},
                {MY_WEIGHT,     200},
                {TAG_DONE,      }
           };

        /* And the mapping list: */
            struct tagitem map[] =
            {
                {MY_SIZE,       HIS_TALL},
                {TAG_DONE,      }
            };

        /* Then after MapTags(list,map,MAP_REMOVE_NOT_FOUND), 'list' will
           become: */
                {HIS_TALL,71},
                {TAG_IGNORE,},
                {TAG_DONE,}

        /* Or after MapTags(list,map,MAP_KEEP_NOT_FOUND), 'list' will
           become: */
                {HIS_TALL,  71},
                {MY_WEIGHT, 200},
                {TAG_DONE,  }

   BUGS
        Prior to V39, the mapType parameter did not work. The function
        always behaved as if the parameter was set to MAP_KEEP_NOT_FOUND.

   SEE ALSO
        <utility/tagitem.h>, applytagchanges(), filtertagchanges()