'Parse a single "<param>" element and return a ToolParameter instance.
Also, if the parameter has a \'required_enctype\' add it to the set
enctypes.'

def parse_param_elem(self, input_source, enctypes, context):

    param = ToolParameter.build(self, input_source)
    param_enctype = param.get_required_enctype()
    if param_enctype:
        enctypes.add(param_enctype)
    for name in param.get_dependencies():
        if (name not in context):
            log.error(("Could    not    find    dependency    '%s'    of    parameter    '%s'    in    tool    %s" % (name, param.name, self.name)))
        context[name].refresh_on_change = True
    return param
