(Ruby; PDF 1.5) A side-note (annotation) written in a smaller text size and placed adjacent to the base text to which it refers. A Ruby element may also contain the RB, RT, and RP elements.
(Ruby) The wrapper around the entire ruby assembly. It shall contain one RB element followed by either an RT element or a three-element group consisting of RP, RT, and RP. Ruby elements and their content elements shall not break across multiple lines.
public static readonly StructureTypeStandard Ruby;