title: "Maximum-Count of Selected Items"-Validator for ListBox
body: <p>i have asked myself if there is an easy way to check if a ListBox has a maximum of 5 selected items. There must be at least one and at most 5 items selected.</p>
  
  <p>Do i need a CustomValidator with server-side validation?</p>
  
  <p>Many thanks in advance...</p>