>There is a variable or field:
>
>

>m.NewValue = MyUnknownVariableOrField
>

>
>How can I tell if MyUnknownVariableOrField is a variable or a field?

Add a m., and use vartype().

If vartype(yourunknown)#'U' and vartype(m.yourunknown)='U'
*  yourunknown is a field
else
*  yourunknown is a memvar
Endif