function empty_check(field){
   if(field.value == ""){
     alert("The value of the field "+field.name+" cannot be empty!");
     field.focus();
     return false;
   }

   return true;
}

function range_check(field,lower,upper,linc,uinc){
   if(linc){
     if(field.value < lower){
       alert("The value of the field "+field.name+" must be greater or equal then "+lower+"!");
       field.focus();
       return false;
     }
   } else {
     if(field.value <= lower){
       alert("The value of the field "+field.name+" must be greater then "+lower+"!");
       field.focus();
       return false;
     }
   }
   if(uinc){
     if(field.value > upper){
       alert("The value of the field "+field.name+" must be less or equal then "+upper+"!");
       field.focus();
       return false;
     }
   } else {
     if(field.value <= upper){
       alert("The value of the field "+field.name+" must be less then "+upper+"!");
       field.focus();
       return false;
     }
   }

   return true;
}

function date_check(field){
   if(isNaN(Date.parse(field.value))){
     alert("The value of the field "+field.name+" has to be a valid date!");
     field.focus();
     return false;
   }

   return true;
}

function email_check(field){
  if(field.value.indexOf("@")==-1){ 
     alert("The email address must contain '@'."); 
     field.focus(); 
     return false; 
  }
  if(field.value.indexOf(",")!=-1 ||
     field.value.indexOf("#")!=-1 ||
     field.value.indexOf("!")!=-1 ||
     field.value.indexOf(" ")!=-1){ 
       alert("Illegal characters in the email address."); 
       field.focus(); 
       return false; 
  }
  if(field.value.length == (field.value.indexOf("@")+1) ) { 
    alert("Email address must have a domain name after the '@'."); 
    field.focus(); 
    return false; 
  }

  return true;
}

function toggle_field(field){
 field.disabled=!field.disabled;

 return field.disabled;
}

function are_you_sure_delete(){
  return confirm("Are you sure you want to delete the selected item?");
}