When you pass in parameters to a Flash or Flex application, you can include most special characters without URL encoding the values.

This includes the following characters:
; / ? : @ $ , # - _ . ! ~ * ' ( )

But as I recently discovered, this doesn’t apply to plus (+) signs.

If you pass in a plus sign as part of a parameter, it will automatically be converted into whitespace. To preserve the plus sign, you need to pass in %2b, which is the URL encoding for a plus sign.