Why is "Four tones (Middle Chinese)" trending?

Wikipedia Overview

The four tones of Chinese poetry and dialectology are four traditional tone classes of Chinese words. They play an important role in Chinese poetry and in comparative studies of tonal development in the modern varieties of Chinese, both in traditional Chinese and in Western linguistics. They correspond to the phonology of Middle Chinese, and are named "even" or "level", "rising", "departing" or "going", and "entering" or "checked" 入; rù)). The last three are collectively referred to as "oblique", an important concept in poetic tone patterns, whereas the first three are collectively referred to as "lax", contrasting with "tense", which is occasionally used in linguistics. Due to historic splits and mergers, none of the modern varieties of Chinese have the exact four tones of Middle Chinese, but they are noted in rhyming dictionaries.