Check format of user-provided 'sections' variable

def _chk_sections(sections):
        """Check format of user-provided 'sections' variable"""
        if sections:
            assert len(sections[0]) == 2, \
                "SECTIONS DATA MUST BE A 2-D LIST. FOUND: {S}".format(S=sections)
            for _, hdrgos in sections:
                chk_goids(hdrgos, "HdrgosSections::_chk_sections()")