filter variable difference

[Danack]

you can filter params in Guzzle like:

{
    "filters": [
        "strtolower",
        {
            "method": "MyClass::convertString",
            "args": [ "test", "@value", "@api" ]
        }
    ]
}

Which would pass to the static function MyClass::convertString three params:

• "test" - a string
• $value - the current value of the param
• $api - which is actually the parameter being operated on.

Which is dumb - it should be called parameter.....

But we should support @parameter, @operation, @api.