Two special Bopomofo IVS fonts from the Bopomofo IVS font specification:
BpmfZihiBox draws each Han character and its Bopomofo reading inside a box,
and BpmfZihiOnly renders only the Bopomofo reading with the Han character
omitted.

They are meant to be used together with a regular Bopomofo IVS font, for
worksheets and other teaching material where the reading has to be shown on
its own or in a ruled frame.

Input methods that implement the Bopomofo IVS specification, such as
chinese/fcitx5-mcbopomofo in its Bopomofo font annotation mode, use these
fonts to produce Bopomofo-annotated text for teaching material and
publishing.