rp

The rp element is used within a ruby element to place parentheses around pronunciation helpers when true rendering of furigana are not supported by the browser.

ruby

The ruby element is used with East Asian written languages in order to place pronunciation helpers adjacent to unfamiliar characters.

rb

The rb element is used within a ruby element to mark the base text that is being annotated.

rt

The rt element is used within a ruby element to place small pronunciation marks next to an East Asian language character.

rtc

The rtc element is used within a ruby element to surround rp and rt elements when they are used semantically, rather than as a pronunciation aid.