The article studies the poetic organization of texts in one of the main genres of Chinese classical literature of the XIII-XIV centuries - the Yuan arias (“ yuanqu ”). We consider two types of lexical units that form the textual structure of the arias - “basic / correct characters” (“ zhengzi ”) and “inserted/adjoining” ones (“ chenzi ”). The paper indicates the difficulties associated with identifying “ chenzi ”. An attempt is being made to establish the reasons that led individual authors of the Yuan arias to deviate from the formal rules prescribed by authoritative medieval literary theorists in special canonical manuals, to violate the recommended poetic size and insert additional words into the lines of their works. The paper identifies the peculiarities of using “inserted” words and examines their possible functions in the works of the Yuan song literature.