NISO has released Recommended Practices for Online Supplemental Journal Article Materials.
Here's an excerpt from the press release:
The National Information Standards Organization (NISO) and the National Federation for Advanced Information Services (NFAIS) have published a new Recommended Practice on Online Supplemental Journal Article Materials (NISO RP-15-2013). Supplemental materials are increasingly being added to journal articles, but until now there has been no recognized set of practices to guide in the selection, delivery, discovery, and preservation of these materials. To address this gap, NISO and NFAIS jointly sponsored an initiative to establish best practices that would provide guidance to publishers and authors for management of supplemental materials and would address related problems for librarians, abstracting and indexing services, and repository administrators. The Supplemental Materials project involved two teams working in tandem: one to address business practices and one to focus on technical issues. This new publication is the combined outcome of the two groups' work.