I recently bought an old manual of how 詞 (classical lyric) are supposed to be "filled". The pages look like this:
Naturally am curious about the meaning of the circle symbols next to each characters and suspect they are related to classical "平／仄" phonology. Indeed ◯ seems associated exclusively with 平声 and ● appears to refer to anything but 平声: specifically 去／入／上声.
However I am baffled about the significance of ◒ and ◓. Analysis of some 菩薩蠻 lyrics indicates that the half-symbols, intuitively enough, mean that either 平/not-平 is allowable in that position in the lyric. For example, the first line of such a lyric has the pattern:
And the following are legal tonal groups (based on a pull of some 词 and conversion of the lyrics to classically defined tonal categories):
平平入入平平入 or 去平平去平平去
In that case what is the difference between ◒ and ◓? Since baidu-ing "circle things AND classical poetry" has not proven fruitful, so thought I would ask for help here. What are those "circle things" even called, properly?