The data Chunk that follows the header Chunk depends on the kind of
Preferences data the file contains.  The types of Preferences data Chunks
that are currently part of the system are:


    Table 13-2: iff chunk types in release 2 preferences data files

    Chunk Name     Used With
    ----------     ---------
       font        fonts, used for all font preferences files.
                   In future the PrefHeader may indicate what the
                   font is used for.
       ictl        icontrol
       inpt        input
       oscn        overscan
       pgfx        printergfx
       ptxt        printertext
       scrm        screenmode
       serl        serial


Each chunk contains a structure applicable to the type.