code: function( elem ) {
  
  		// No argument, return index in parent
  		if ( !elem ) {
  			return ( this[ 0 ] && this[ 0 ].parentNode ) ? this.first().prevAll().length : -1;
  		}
  
  		// index in selector
  		if ( typeof elem === "string" ) {
  			return indexOf.call( jQuery( elem ), this[ 0 ] );
  		}
  
  		// Locate the position of the desired element
  		return indexOf.call( this,
  
  			// If it receives a jQuery object, the first element is used
  			elem.jquery ? elem[ 0 ] : elem
  		);
  	}
docs: Determine the position of an element within the matched set of elements