code: JCExpression annotationFieldValue() {
          if (LAX_IDENTIFIER.accepts(token.kind)) {
              mode = EXPR;
              JCExpression t1 = term1();
              if (t1.hasTag(IDENT) && token.kind == EQ) {
                  int pos = token.pos;
                  accept(EQ);
                  JCExpression v = annotationValue();
                  return toP(F.at(pos).Assign(t1, v));
              } else {
                  return t1;
              }
          }
          return annotationValue();
      }
docs: AnnotationFieldValue    = AnnotationValue
  | Identifier "=" AnnotationValue