Optional. The default value to use when the value yields an empty result. Default values can be extracted from contexts by using the following syntax: #context_name.parameter_name.
Optional. The definition of the parameter value. It can be: - a constant string, - a parameter value defined as $parameter_name, - an original parameter value defined as $parameter_name.original, - a parameter value from some context defined as #context_name.parameter_name.