Checks for the presence of an attribute in a request. You can use either exact match or alternation. Attribute value does not matter; empty attributes match too. This type of check item is mostly useful in Handlers

<Handler ExistsInRequest = EAP-Message>
    # All EAP messages are handled here
</Handler>

<Handler ExistsInRequest = OSC-Rate-Limit-Day|OSC-Rate-Limit-Night>
    # Handler is selected when one or the both are present
</Handler>