// UpdateMusicButton : update the music button image depending on its status or hide it if no frame is detected function UpdateMusicButton()  {   if( document.MusicButton )   {	 		if( parent && parent.musicFrame ) 		{ 			if( parent.MusicOn ) 				document.MusicButton.src = '../_frame/music.png'; 			else 				document.MusicButton.src = '../_frame/nomusic.png'; 			} 		else 			document.MusicButton.style.display = 'none'; 	} }  // MusicPlay : play or stop a music depeinding on its topic name // topic = "_stop_" is a dummy topic name meaning that there is no music and that any playing music has to be stopped // topic = "" (an empty topic) means a topic witout any music but that should continue playing any previous music  // for any other value the music page of the topic specified is used. This can be the reserved directory "_frame" in the case of a music played for the entire website function MusicPlay( topic )  {   if( parent && parent.musicFrame )    { 		if( topic == "_stop_" ) // topic has no music so we redirect the silent index.html page located under the _frame directory 		{       parent.MusicPageURL = '../_frame/blank.html';       parent.musicFrame.location = parent.MusicPageURL; 		} 		else 		{ 		  //  if any topic name is specified we use the url of its music page otherwise we do nothing meaning that we continue to use the previous music page 			if( topic != '' ) 				parent.MusicPageURL = '../' + topic + '/music.html'; 			if( parent.MusicOn )  			{ 				parent.musicFrame.location = '../_frame/blank.html'; 				parent.MusicOn = 0; 			} 			else if( parent.MusicPageURL != '' ) 			{ 				parent.musicFrame.location = parent.MusicPageURL; 				parent.MusicOn = 1; 			} 		} 		if( parent.MusicPageURL != '' )       UpdateMusicButton();   } }