2.1.531 Part 4 Section 18.104.22.168, SYMBOL
a. The standard says the \j switch interprets text in the field argument as the value of a SHIFT-JIS character.
If the \j switch is used with characters 0x5C or 0x7E, Word does not display their SHIFT-JIS substitutions.
b. The standard places no restrictions on the Unicode characters which may be used with the \u switch in the SYMBOL field.
Using the \u switch, Word will not display surrogate pairs or Unicode characters outside of Unicode plane 0 (Basic Multilingual Plane). If a character is specified outside of plane 0, the value will be truncated to one within plane 0.
c. The standard allows the SYMBOL field to be nested inside another field.
In Word, if the SYMBOL field is nested inside another field, no result is displayed.