Concatenates a list of Digital Form data structures parsed from the metadata

def _parse_digital_forms(self, prop=DIGITAL_FORMS):
        """ Concatenates a list of Digital Form data structures parsed from the metadata """

        xpath_map = self._data_structures[prop]

        # Parse base digital form fields: 'name', 'content', 'decompression', 'version', 'specification'
        xpath_root = self._data_map['_digital_forms_root']
        digital_forms = parse_complex_list(self._xml_tree, xpath_root, xpath_map, prop)

        # Parse digital form transfer option fields: 'access_desc', 'access_instrs', 'network_resource'
        xpath_root = self._data_map['_transfer_options_root']
        transfer_opts = parse_complex_list(self._xml_tree, xpath_root, xpath_map, prop)

        # Split out digital form content that has been appended to specifications

        content_delim = _DIGITAL_FORMS_CONTENT_DELIM

        for digital_form in digital_forms:
            specs = reduce_value(digital_form['specification'])
            specs = specs.splitlines() if isinstance(specs, string_types) else specs

            specifications = wrap_value(s.strip() for s in specs)

            digital_form['content'] = []
            digital_form['specification'] = []
            has_content = False

            # For each specification, insert delim before appending content
            for spec in specifications:
                has_content = has_content or spec == content_delim

                if not has_content:
                    digital_form['specification'].append(spec)
                elif spec != content_delim:
                    digital_form['content'].append(spec)

            # Reduce spec and content to single string values if possible
            for form_prop in ('content', 'specification'):
                digital_form[form_prop] = reduce_value(filter_empty(digital_form[form_prop], u''))

        # Combine digital forms and transfer options into a single complex struct

        df_len = len(digital_forms)
        to_len = len(transfer_opts)
        parsed_forms = []

        for idx in xrange(0, max(df_len, to_len)):
            digital_form = {}.fromkeys(_iso_definitions[prop], u'')

            if idx < df_len:
                digital_form.update(i for i in digital_forms[idx].items() if i[1])
            if idx < to_len:
                digital_form.update(i for i in transfer_opts[idx].items() if i[1])

            if any(digital_form.values()):
                parsed_forms.append(digital_form)

        return get_default_for_complex(prop, parsed_forms)