Mixing fullwidth and halfwidth punctuation throws the beat off

What it is

A fullwidth comma occupies an em. A halfwidth comma occupies about half. Alternate them on one line and the beat of the clause marks goes wide, then tight. Punctuation rhythm is that beat. It is not the question of a gap between Han and Latin, nor of whether baselines agree. Mixing the two marks breaks the even “character—mark—character” pulse, and the line looks as if two drummers had taken turns.

Why it happens

Chinese body time is the em. Fullwidth punctuation pauses in that unit; enumeration commas, commas, periods form expected breaths, and the line’s grey steps on the character grid. Halfwidth punctuation is borrowed from Latin: width, position, and side gaps follow the half-space system, and dropped into an em grid they skip half a beat. Input methods, paste from English copy, and programmatic joins of prices and units are the three doors halfwidth marks use to enter a Chinese line. Once the beat is off, kinsoku classes go off too: some engines do not treat a halfwidth period as a line-start-prohibited character, and they do treat the fullwidth one. The same semantic dot then refuses to start a line in fullwidth and will start a line in halfwidth — it looks like a wrap bug, and the root is a mixed character class. This claim is about the mark as metronome and as kinsoku class. It does not own the gap between CJK and Latin words, and it does not own x-height versus Han alignment.

Where it stops holding

A Chinese sentence that quotes an English proper name should keep that name’s halfwidth apostrophe or hyphen; do not fullwidth O'Reilly for consistency. Code, regexes, and keystrokes stay halfwidth. A sentence that is entirely English should use halfwidth marks, then switch back to fullwidth when the body is Chinese again — the switch sits on the language boundary, not on each mark inside one Chinese clause. A fullwidth space used as “alignment” beside punctuation adds a fake extra beat, worse than a mixed comma.

Applying it

• Standardize Chinese body on fullwidth clause marks. Normalize punctuation on strings spliced in from English before they enter a Chinese line.
• Set a live sentence that mixes , with ， and . with 。 on one line and look at whether the breaths are even. If they are not, two kinds of mark are fighting for the beat; it is not a style choice.
• Check whether a halfwidth period can start a line when a fullwidth period never does. Either fold the halfwidth mark into the same kinsoku class or replace it with fullwidth.

Related

• Same group: F4.14.1 Closing CJK punctuation must not start a line · F4.14.2 Opening brackets and quotes must not end a line · F4.14.3 Kinsoku needs an engine; a naive wrap will break it
• Nearby: F4.06 Mixed CJK and Latin typesetting · F4.12 Tracking and word spacing
• Search terms: fullwidth punctuation · punctuation rhythm · halfwidth comma