2.2.3 [W3C-RUBY] Section 2.5, The rb element
The specification states:
The rb (ruby base) element serves to markup the base text. For simple ruby markup, only one rb element may appear. For complex ruby markup, multiple rb elements may appear inside an rbc element. Each rb element is associated with a corresponding rt element, for fine-grained control of ruby presentation.The rb element may contain inline elements or character data as its content, but the ruby element is not allowed as its descendant element.
All Document Modes (All Versions)
The following clarifications apply:
All rb elements within simple or complex ruby elements are displayed.
No error handling occurs for an rb element with a descendant ruby element.