code: function prepareElementHidden() {
  
          var name
  
          if ( SETTINGS.hiddenName === true ) {
              name = ELEMENT.name
              ELEMENT.name = ''
          }
          else {
              name = [
                  typeof SETTINGS.hiddenPrefix == 'string' ? SETTINGS.hiddenPrefix : '',
                  typeof SETTINGS.hiddenSuffix == 'string' ? SETTINGS.hiddenSuffix : '_submit'
              ]
              name = name[0] + ELEMENT.name + name[1]
          }
  
          P._hidden = $(
              '<input ' +
              'type=hidden ' +
  
              // Create the name using the original input’s with a prefix and suffix.
              'name="' + name + '"' +
  
              // If the element has a value, set the hidden value as well.
              (
                  $ELEMENT.data('value') || ELEMENT.value ?
                      ' value="' + P.get('select', SETTINGS.formatSubmit) + '"' :
                      ''
              ) +
              '>'
          )[0]
  
          $ELEMENT.
  
              // If the value changes, update the hidden input with the correct format.
              on('change.' + STATE.id, function() {
                  P._hidden.value = ELEMENT.value ?
                      P.get('select', SETTINGS.formatSubmit) :
                      ''
              })
  
  
          // Insert the hidden input as specified in the settings.
          if ( SETTINGS.container ) $( SETTINGS.container ).append( P._hidden )
          else $ELEMENT.after( P._hidden )
      }
docs: Prepare the hidden input element along with all bindings.