[2] In Li's 1985 paper, he suggested using tonal reflexes of Middle Chinese checked tone characters as the criterion for classifying Mandarin dialects.

[3] In this paper, he used the term "Beijing Mandarin" (北京官话) to refer the dialect group in which checked tone characters with a voiceless initial have dark level, light level, rising and departing tone reflexes.

[1][13] Dental and retroflex sibilants are distinct phonemes in Beijing Mandarin.

[5] This is contrary to Northeastern Mandarin, in which the two categories are either in free variation or merged into a single type of sibilants.

[18] The Cháo–Fēng subgroup generally has a lower tonal value for the dark level tone.