function checkdate(input, annoying){
	if(input.value.length==0) return true;
  	var validformat=/^\d{4}-\d{2}-\d{2}$/ //Basic check for format validity
  	var returnval=false
  	
  	if (!validformat.test(input.value))		alert("Niewłaściwy format daty (poprawny: rrrr-mm-dd).")
  	else{
		var monthfield=input.value.split("-")[1]
		var dayfield=input.value.split("-")[2]
		var yearfield=input.value.split("-")[0]
		var dayobj = new Date(yearfield, monthfield-1, dayfield)
		if ((dayobj.getMonth()+1!=monthfield)||(dayobj.getDate()!=dayfield)||(dayobj.getFullYear()!=yearfield))
			alert("Nieprawidłowa data.")
		else
			returnval=true
  	}
  	
 	if (returnval==false && annoying==1) input.select()
 	
 return returnval
}