Closing CJK punctuation must not start a line

What it is

Commas, periods, enumeration commas, semicolons, exclamation and question marks, closing quotes, closing parentheses — these are the tail of a clause, not the start of one. Parked at the left edge they make the previous line look unfinished and the new line look as if it began mid-breath. Chinese and Japanese setting lists them under kinsoku line-start prohibition: pull the preceding character down with them rather than let those marks open the door alone.

Why it happens

A clause mark attaches to the character before it. Visually it is that character’s close, not the next idea’s start. A wrap that cuts whenever width runs out can split between character and mark, and the mark is shoved to the next line’s head. Line scanning begins at the leading edge; an isolated 。 or ， there anchors on a closer, not a character, and the beat skips. Print makes the prohibition mandatory: set one fewer character on the previous line, or let the mark hang slightly outside the measure, in exchange for a clean line head. On screens, greedy wrapping has no kinsoku, so leading-edge periods cluster in narrow columns, large type, and justified setting — all of which raise the odds of cutting just before a mark.

Where it stops holding

Latin almost never starts a line with a closing quote or period, because a word space already kept the mark with the word; this claim is about unspaced Han lines. Ellipses, dashes, and connectors vary by tradition; do not extend the comma/period ban to every mark. Code, formulae, and monospaced logs wrap on a character grid; kinsoku yields to alignment. In vertical setting the “line head” is the top of the column; the same marks still must not open a run.

Applying it

• Turn on the engine’s line-start kinsoku (or an equivalent strict wrap) for Chinese body. Do not wrap on width alone.
• Pour punctuation-heavy help copy into the narrowest column at the largest type and watch the first character of every line. A comma or period there is a hit.
• If the platform can hang punctuation, keep the clause mark on the previous line that way, rather than dragging the previous character down and leaving a hole.

Related

• Same group: 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 · F4.14.4 Mixing fullwidth and halfwidth punctuation throws the beat off
• Nearby: F4.03 Measure · F4.06 Mixed CJK and Latin typesetting
• Search terms: kinsoku · line-start punctuation · CJK line breaking