Ruby
Ruby can be expressed by -ah-display: ruby, -ah-display: ruby-base and -ah-display: ruby-text. -ah-display: ruby-base maps to one -ah-display: ruby-text. A pair of one -ah-display: ruby-base and -ah-display: ruby-text is called the ruby container and multiple ruby containter are set within -ah-display: ruby-base. A ruby has 3 forms, and it's classified as follows.

Mono-ruby

The ruby container of mono-ruby is independent and ruby characters never overhang the base character of the adjacent ruby.
京きよう 都と 府ふ

Group-ruby

Group-ruby consists of one ruby container. Group-ruby is evenly arranged to the entire base characters.
京都府きようとふ

Jukugo (kanji compound word) - ruby

Jyukugo-ruby consists of one or more ruby containers. when the ruby text is wider than the ruby base characters, ruby text is allowed to partially overhang any adjacent text in addition to its own base to adjust its position.
京きよう都と府ふ
鬼門の方角を 凝ぎよう視し する。