Takes two parameters, Source, AllowedCharacters (case sensitive)
This command determines if all of the characters in the Source parameter are also included in the AllowedCharacters parameter. If all characters in Source are in AllowedCharacters, an empty string will be returned. If any of the characters in the Source parameter are not in the AllowedCharacter parameter, then the index where the first invalid character was encountered in the Source parameter will be returned.
This is a similar command to Verify$, which returns the index of the first invalid character as a string.
[New] source = "Alex"
[New] allowedCharacters = "Alx"
[New] result = Verify$ source, allowedCharacters
Html ("result: " & result) 'result is equal to "3"