users may use this method to validate the value of the parameter
in the request
for eg: the parameter value must contain NYC or it must not contain XYZ
or they may even validate it against the custom expression
set optionally.
validate that a string is a W3C binary type
validate returns true or false depending on whether the string content is an
instance of the W3C binary datatype
This method is different from "validateContent" in that it will try to use
the SubstitutionGroupComparator to match children against the content model.