Support of new CSS property `ruby-overhang` is added. The property accepts one of `auto`, `spaces` and `none` keywords to control overhang of ruby annotation text. Per CSSWG, none is aliased to spaces, allowing overhang only over whitespace and CJK punctuation. This prevents unnecessary layout gaps while preserving text readability.
A ruby annotation can sometimes obscure adjacent content when it overhangs. The ruby-overhang property gives authors a way to disable this behavior and prevent unwanted overlap. For example, in children's books or text books for low-vision readers, authors need to ensure none overhang to prevent any reading confusion.