Recently on the OpenType list, a question was asked about handling the differences between certain CJK punctuation within a single font for correctly displaying horizontal Japanese and Chinese text in the same file.
John Hudson offered a solution for this issue. How do these differences apply to Unicode plain text and the Plane 14 tags? For example, it was noted that the ideographic full stop is centered in Chinese text but sits on the baseline (and isn't centered) in Japanese text. Without a plain text method of distinguishing the writing system for a run of text, a plain text file wouldn't be able to be correctly displayed if it had both Japanese and Chinese text. (Ideographic variants notwithstanding.) Best regards, James Kass.
