The content types with metadata
        @return: ['application/xxx', ...]

def listMetaContentTypes(self):
        """The content types with metadata
        @return: ['application/xxx', ...]
        """

        all_md_content_types = (
            CT_CORE_PROPS,
            CT_EXT_PROPS,
            CT_CUSTOM_PROPS)
        return [k for k in self.overrides.keys() if k in all_md_content_types]