First, XBRL is XML. See:XBRL most certainly does use XML Schema - and then some:.

As for taxonomy management, I couldn't find an explicit package, and the reason seems to be interoperability---between, on the one hand, differing taxonomies and differing vendors---and, on the other hand, differing methods of dealing with whitespace and with numbers for validation by XML Schema---However, the specification is clearly defined, and XBRL is absolutely necessary for the financial system to work properly, so I was surprised that there aren't any modules that can, for example, manage a taxonomy.

See: BestPractices for more info.