Assume name/value pairs of Strings (UTF-8)? Value optional.
Consider whether annotations is something separate (probably not - just use value field).
Need to optionally refer to specific path & version, or default to latest version, whole object etc.
Target can be any VERSIONED object. Reference is an OBJECT_VERSION_ID [+ path]
Need to consider some core set of standard tag names - mod to terminology ?? (Not necessary for this CR)