<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _process_extensions(exts):
 """ Generate the `Extensions String` from an iterable of data forms. :param exts: The data forms to generate the extensions string from. :type exts: :class:`~collections.abc.Iterable` of :class:`~.forms.xso.Data` :return: The `Extensions String` :rtype: :class:`bytes` Generate the `Extensions String` from the given `exts` as specified in :xep:`390`. """

    parts = [
        _process_form(form)
        for form in exts
    ]
    parts.sort()
    return b"".join(parts)+b"\x1c"