Histone demethylase that specifically demethylates 'Lys-27' of histone H3, thereby playing a central role in histone code (PubMed:17713478, PubMed:17825402, PubMed:17851529, PubMed:18003914). Demethylates trimethylated and dimethylated H3 'Lys-27' (PubMed:17713478, PubMed:17825402, PubMed:17851529, PubMed:18003914). Plays a central role in regulation of posterior development, by regulating HOX gene expression (PubMed:17851529). Involved in inflammatory response by participating in macrophage differentiation in case of inflammation by regulating gene expression and macrophage differentiation (PubMed:17825402). Plays a demethylase-independent role in chromatin remodeling to regulate T-box family member-dependent gene expression by acting as a link between T-box factors and the SMARCA4- containing SWI/SNF remodeling complex (By similarity). {ECO:0000250|UniProtKB:Q5NCY0, ECO:0000269|PubMed:17713478, ECO:0000269|PubMed:17825402, ECO:0000269|PubMed:17851529, ECO:0000269|PubMed:18003914, ECO:0000269|PubMed:28262558}. This is the function of Ensembl gene identifier ENSG00000132510 (KDM6B, lysine demethylase 6B).