Gugyeol, or kwukyel, is a system for rendering texts written in Classical Chinese into understandable Korean.
Thus, in gugyeol, the original text in Classical Chinese was not modified, and the additional markers were simply inserted between phrases.
This name is itself believed to originate from the use of hanja characters to represent the Middle Korean phrase ipgyeot (입겿), with a similar meaning.
The later version of the gugyeol system was formalized by Chŏng Mong-ju and Kwŏn Kŭn around 1400 in the early Joseon Dynasty, at the behest of King Taejong.
In this respect, gugyeol remains in occasional use in contemporary South Korea, where such techniques are still sometimes used to render the Confucian classics into readable form.