The Fld structure specifies a field character.
fldch (1 byte): An fldch whose ch member controls the interpretation of grffld. This value MUST be 0x13, 0x14, or 0x15.
grffld (1 byte): The meaning of this field is dependent on the value of fldch, as defined following.
grffld is an unsigned integer that indicates the kind of field this was the last time that an application parsed it. The values are specified in flt.
grffld is unused and MUST be ignored.
grffld is a grffldEnd.