code: public HeadedSyntacticCategory getArgumentType() {
      SyntacticCategory argumentSyntax = syntacticCategory.getArgument();
      int[] argumentSemantics = ArrayUtils.copyOfRange(semanticVariables, rootIndex + 1, semanticVariables.length);
      int argumentRoot = argumentSyntax.getNumReturnSubcategories();
      return new HeadedSyntacticCategory(argumentSyntax, argumentSemantics, argumentRoot);
    }
docs: Gets the syntactic type and semantic variable assignments to the
  argument type of this category.
  
  @return