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Tips
history
坊 originally meant a walled residential ward in Tang-era cities — Chang'an was divided into 108 such 坊. 坊间 literally "between the wards" came to mean "out in the street / among the people," hence today's sense of unofficial, popular circulation.
register
Slightly literary. Common in news headlines: 坊间传闻 (street rumor), 坊间流传 (circulating among the public). Don't use it for your living room.