title: How to filter the Application.OpenForms collection with Linq?
body: <p>I would like to use <code>Where</code> to filter the <code>Application.OpenForms</code> collection with Linq, and several questions on this site  <a href="https://stackoverflow.com/questions/1688794/linq-expression-to-filter-formcollection">[1]</a> <a href="https://stackoverflow.com/questions/3831606/getting-all-selected-checkboxes-from-a-formcollection">[2]</a> <a href="https://stackoverflow.com/questions/4893147/slicing-a-formcollection-by-keys-that-start-with-a-certain-string">[3]</a> suggest that all I that need in order to do that is access its <code>AllKeys</code> property. However, even when I create a new Windows Forms application, the collection doesn't seem to have this property at all and doesn't compile when I try to use it. What could be the reason?</p>