docs: function(funcName, expr, sup, sub) {
                      this.callBase();
                      this.setFlag("Func");
                      this.funcName = funcName;
                      this.setOperator(new FunctionOperator(funcName));
                      this.setExpr(expr);
                      this.setSuperscript(sup);
                      this.setSubscript(sub);
                  }