Catalysis of the reaction: 2,3-dihydroxybenzenoid + O2 = H+ + distal extradiol ring cleavage. Substrates are 2,2',3-trihydroxybiphenyl (forms 2-hydroxy-6-oxo-6-(2-hydroxyphenyl)-hexa-2,4-dienoate) and 2,2',3-trihydroxydiphenylether (forms 2,3-hydroxy-6-oxo-6-(2-hydroxyphenyl)-hexa-2,4-dienoate).