function set_attribute(element_id, attribute, value) {
      var element = document.getElementById(element_id);
      element.setAttribute(attribute, value);
   }


   function get_attribute(element_id, attribute) {
      var element = document.getElementById(element_id);
      return element.getAttribute(attribute);
   }
   
   function set_style(element_id, property, style) {
      var element = document.getElementById(element_id);
      element.style[property] = style;
   }

   function set_display(element_id, display_style) {
      var element = document.getElementById(element_id);
      element.style.display = display_style;
   }
   
   function append_child(element_id, child_tag, child_id) {
      var element = document.getElementById(element_id);
      var child = document.createElement(child_tag);
      child.setAttribute('id', child_id);
      element.appendChild(child);
   }

   function remove_child(element_id, child_id) {
      var element = document.getElementById(element_id);
      var child = document.getElementById(child_id);
      element.removeChild(child);
   }