New answers tagged orthography
There are basic rules about the use of commas in Japanese but these are not absolute. I think a writer can use commas as they like to make a sentence easier to read. And I don't think there is a clear rule in Japanese as you say.
⇳ (The upper image from: http://p.twipple.jp/zAedi; the lower from: http://portal.nifty.com/cs/mitaiwa/detail/100607127809/1.htm)
If the text has been laid out properly by a designer the words will wrap right after the particle for more natural flow (が、を、は etc). For a websites in Japanese, because there is no whitespace between characters the sentence is treated as one 'word' and will break wherever it needs to.
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