The Program for Cooperative Cataloging (PCC) Standing Committee on Training (SCT) published a training manual for applying relationship designators in bibliographic records in January 2015. See http://www.loc.gov/aba/pcc/sct/documents/rel-desig-guide-bib.pdf.
New relationship designators may be proposed using the PCC relationship designator proposal form. See http://www.loc.gov/aba/pcc/scs/RD-Requests.html.
Please use MOUG-L to discuss ideas for new or revised relationship designators, or contact any of the following people:
Kathy Glennan, ALA representative to the Joint Steering Committee
Beth Iseminger, Chair of MLA Cataloging and Metadata Committee
Tracey Snyder, Chair of MLA Content Standards Subcommittee