Back to the binaries! Yeah!

After all this XML work the binary file formats are a different world. For the fields work I needed to analyze the “form field” structure of the binary .DOC format:

The header: Actually a misused PICT structure:

b10	b16	field	Type	size	bitfield	comments
0	0	lcb	U32			Count of bytes of the whole block.
4	4	cbHeader	U16			Always 0x44
6	6		U8[62]			Contains zero. In fact this is the PICT struct, but since its not need we can fill it with zeros.

The formfield payload (Unicode Variant)

b10	b16	Field	Type	size	bitfield	comments
0	0	cUnicodeMarker	U8[32]			Contains {0xFF,0xFF,0xFF,0xFF}
4	4	fftype	U8	:2	03	Type: 0 = Text 1 = Check Box 2 = List
		ffres	U8	:5	7C	Result field for a form field. Values from 0 to N-1, where N is the number of \ffl entries. In case of check boxes: 0==unchecked; 1==checked.
		ffownhelp	U8	:1	80	1 if there is associated Help text, 0 otherwise.
5	5	ffownstat	U8	:1	01	1 if there is associated status line text, 0 otherwise.
		ffprot	U8	:1	02	1 if this field is protected, 0 otherwise.
		ffsize	U8	:1	04	Type of size selected for check box field: 0 = Auto 1 = Exact
		fftypetxt	U8	:3	38	Type of text field: 0 = Regular text 1 = Number 2 = Date 3 = Current date 4 = Current time 5 = Calculation
		ffrecalc	U8	:1	40	1 if the field should be calculated on exit, 0 otherwise.
		ffhaslistbox	U8	:1	80	1 if this field has list box attached to it, 0 otherwise.
6	6	ffmaxlen	U16	:15	7FFF	Number of characters for text field. Zero means unlimited.
			U16	:1	8000	Unknown. Set to zero.
8	8	ffhps	U16			Check box size (half-point sizes).
10	A	xstz_ffname	Xstz_UString0			Form field name
		xstz_ffddeftext	Xstz_UString0			Default text for field. Only if type==0.
		ffdefres	U16			Default resource for list field. Default value for check box (0=default unchecked; 1=default checked). Only if type!=0.
		xstz_ffformat	Xstz_UString0			Format for text field
		xstz_ffhelptext	Xstz_UString0			Help text
		xstz_ffstattext	Xstz_UString0			Status line text
		xstz_ffentrymcr	Xstz_UString0			Macro to execute upon entry into this form field
		xstz_ffexitmcr	Xstz_UString0			Macro to execute upon exit from this form field
		cUnicodeMarker2	U8[2]			Contains {0xFF, 0xFF}; Padding and/or indicator for Unicode?
		fflLen	U32			Num of ffls
		ffl	Xstz_UString[fflLen]			Resource string for lists.

An Xstz_UString has the following form:

b10	B16	Field	type	size	bitfield	Comments
0	0	Len	U16			Len of the String.
2	2	Unicode char	U16[len]			Unicode chars

An Xstz_UString0 has the following form:

b10	B16	Field	type	size	bitfield	Comments
0	0	len	U16			Len of the String.
2	2	Unicode char	U16[len]			Unicode chars
2+2*len		Zero	U16			Trailing “0”

In case of non-Unicode encoding then the Unicode Marker disappear and the string chars have U8 size.

You might also want to take a look at the ffData element in OOXML ;-)