title: How to validate Parameters against a long set in PowerShell?
body: <p>I am writing a script which will accept a few parameters. I need to validate one parameter that user will have to enter. I use for <code>[ValidateSet(...)]</code> feature of <code>Param</code> block. 
  However, I need to validate this parameter against a very long <code>hash table</code>.
  Since my hash table is declared after <code>Param</code>, How do I validate the user inputs against the keys of that hash table?</p>