This paper looks at a subset of metadata schemes, including the Text Encoding Initiative (TEI) header, the Encoded Archival Description (EAD), the Dublin Core Metadata Element Set (DCMES), and the Visual Resources Association (VRA) Core Categories for visual resources. It examines why they developed as they did, major point of difference from traditional library cataloging, and what advantages they offer to their user communities. It also discusses challenges to implementers of these schemes and possible developments. It goes on to identify some commonalities among these cases and to attempt to generalize from these some lessons for developers of metadata element sets. It concludes by suggesting the importance of looking carefully at emerging schemes being developed by publishers in support of electronic commerce and rights management and thinking seriously about the implications of commodity metadata upon tradition bibliographic apparatus. (Contains 18 notes.) (MES)