IVOA Recommendation: Maintenance of the list of UCD words Version 1.20

According to what is stated in the IVOA Recommendation “An IVOA standard for Unified Content Descriptors”, a procedural document should be created in order to maintain (add, change, suppress words) the standard list of UCD1+ words “The UCD1+ Controlled Vocabulary”. This document describes the procedure to maintain the standard list of UCD1+ words.