Update operation for ISO Digital Forms metadata
        :see: gis_metadata.utils._complex_definitions[DIGITAL_FORMS]

def _update_digital_forms(self, **update_props):
        """
        Update operation for ISO Digital Forms metadata
        :see: gis_metadata.utils._complex_definitions[DIGITAL_FORMS]
        """

        digital_forms = wrap_value(update_props['values'])

        # Update all Digital Form properties: distributionFormat*

        xpath_map = self._data_structures[update_props['prop']]

        dist_format_props = ('name', 'decompression', 'version', 'specification')
        dist_format_xroot = self._data_map['_digital_forms_root']
        dist_format_xmap = {prop: xpath_map[prop] for prop in dist_format_props}
        dist_formats = []

        for digital_form in digital_forms:
            dist_format = {prop: digital_form[prop] for prop in dist_format_props}

            if digital_form.get('content'):
                dist_spec = wrap_value(digital_form.get('specification'))
                dist_spec.append(_DIGITAL_FORMS_CONTENT_DELIM)
                dist_spec.extend(wrap_value(digital_form['content']))
                dist_format['specification'] = dist_spec

            dist_formats.append(dist_format)

        update_props['values'] = dist_formats
        dist_formats = update_complex_list(
            xpath_root=dist_format_xroot, xpath_map=dist_format_xmap, **update_props
        )

        # Update all Network Resources: transferOptions+

        trans_option_props = ('access_desc', 'access_instrs', 'network_resource')
        trans_option_xroot = self._data_map['_transfer_options_root']
        trans_option_xmap = {prop: self._data_map['_' + prop] for prop in trans_option_props}

        trans_options = []
        for digital_form in digital_forms:
            trans_options.append({prop: digital_form[prop] for prop in trans_option_props})

        update_props['values'] = trans_options
        trans_options = update_complex_list(
            xpath_root=trans_option_xroot, xpath_map=trans_option_xmap, **update_props
        )

        return {
            'distribution_formats': dist_formats,
            'transfer_options': trans_options
        }