The PPRF chunk contains preference settings for ProVector.  Although
this chunk is not required, its use is encouraged because it contains
some important environment information.

    struct PPRFstruct {
        ULONG       ID;
        ULONG       Size;
        char        Prefs[Size];
    };

DR2D stores preferences as a concatenation of several null-terminated
strings, in the Prefs[] array.  The strings can appear in any order.
The currently supported strings are:

            Units=<unit-type>
            Portrait=<boolean>
            PageType=<page-type>
            GridSize=<number>

where:
            <unit-type>     is either Inch, Cm, or Pica
            <boolean>       is either True or False
            <page-type>     is either Standard, Legal, B4, B5, A3,
                              A4, A5, or Custom
            <number>        is a floating-point number

The DR2D FORM does not require this chunk to explicitly state all the
possible preferences.  In the absence of any particular preference
string, a DR2D reader should fall back on the default value.  The
defaults are:

            Units=Inch
            Portrait=True
            PageType=Standard
            GridSize=1.0