function isset(varname){
	  return(typeof(window[varname])!='undefined');
	}

	function changeTab( tabId ) {
	  var visivel       = '';
	  var invisivel     = 'none'; 

	  if ( !isset( 'tabs' ) )
	  {
	  	alert( "Variável tabs não está definida." );
	  } else {
		  for (var x = 1; x <= tabs; x++)
	    {
				if (document.getElementById( 'tab' + x ) != null) 
				{
				  document.getElementById( 'tab' + x ).style.display = invisivel;
				  document.getElementById( 'tabId' + x ).style.background = "#D8D8D8";
				  document.getElementById( 'tabId' + x ).style.border = "1px solid #a0a0a0";
				}
		  }
		
		  document.getElementById( 'tab' + tabId ).style.display = visivel;
		  document.getElementById( 'tabId' + tabId ).style.background = "#ffffff";
		  document.getElementById( 'tabId' + tabId ).style.borderBottom = "1px solid #ffffff";
	  }
	}
	
	changeTab( 1 );