2.1.272 Part 1 Section 18.104.22.168, sig (Supported Unicode Subranges and Code Pages)
a. The standard states that the sig element shall not be modified when the font is an unknown font.
For unknown fonts, if the font cannot be resolved using the alternate font name or character set, Word might incorrectly reset bits to 0 in the usb0 attribute when bits in the csb0 attribute are set.
b. The standard states that when a font is unavailable the sig element shall not be modified.
Word can modify the sig element of an unavailable font if a font with the same name has been loaded before in the same Word instance.
c. The standard states that the csb0 and csb1 attributes are specified as four-digit hexadecimal encodings.
Word expects the csb1 and csb2 attributes to be eight-digit hexadecimal encodings.