code: public boolean push(final int down, final V value)
      {
          check();
          context.getValueStack().push(down, value);
          return true;
      }
docs: Inserts the given value a given number of elements below the current top
  of the value stack
  
  @param down the number of elements to skip before inserting the value (0
  being equivalent to {@code push(value)})
  @param value the value
  @return true
  
  @throws IllegalArgumentException the stack does not contain enough
  elements to perform this operation