Should flag

Narrow justified paragraph, no hyphenation

300px column, about 37 characters per line

Forcing every line of a column this narrow out to the same width leaves only a handful of word spaces to carry the slack, so each one opens up until the gaps line up vertically and a river of white runs down the paragraph.

Narrow justified paragraph with hyphens: manual

260px column, hyphenation only where the author typed a soft hyphen

Setting hyphens to manual leaves the breaking to the author, so an unmarked word still travels whole to the next line and the line it left behind stretches to cover the distance it used to fill.

Justified sidebar column

Should pass

Justified at a long measure

760px column, about 95 characters per line

At a long measure there are enough word spaces on every line that the leftover width spreads thinly across all of them, which is why books and newspapers have justified comfortably for centuries without anyone seeing a river in the page.

Narrow justified paragraph with hyphens: auto

300px column, automatic hyphenation on

With automatic hyphenation the browser breaks the long words itself, so every line ends close to the margin already and justification has almost nothing left to stretch.

Narrow justified Chinese paragraph

300px column, characters of uniform width

永慶房屋於一九八八年成立,專注本業,堅持創新,秉持先誠實再成交的精神,提供消費者透明的資訊與安心的服務,目前在雙北地區有逾二百八十家直營門市。

Narrow justified Thai paragraph

300px column, no spaces between words to stretch

การจัดวางข้อความแบบชิดขอบทั้งสองด้านในภาษาไทยไม่ได้ดึงช่องว่างระหว่างคำให้กว้างขึ้นเพราะโดยปกติแล้วภาษาไทยไม่ได้เว้นวรรคระหว่างคำในประโยคเดียวกัน

Narrow justified Arabic paragraph

300px column, justified by elongating glyphs

يعتمد ضبط النص في الخط العربي على استطالة الحروف على السطر بدلا من توسيع المسافات بين الكلمات، ولذلك تبقى المسافات متساوية ولا تظهر تلك الفجوات البيضاء الممتدة عبر الفقرة.