[dba-Tech] Entering Word field codes

I can't quite figure out what characters I can enter manually in a field code. For instance, Word didn't like it when I tried to enter the = for a formula field code, so I get that it wants to control that. But, it let me add a + 1 component -- anyone have the skinny on that? I don't want to make this harder than necessary. 

As an after thought -- is it possible to enter the entire code manually and then somehow identify or format it as a field code? 

Susan H.