In the lyrics of folk songs, in addition to the main words that directly express the ideological content of the song, there are often some foiling words and sentences composed of modal particles, ideograms or titles. Most of them are not directly related to the main words. They do not fall within the basic sentence structure of the main words, and even many of them are unintelligible words and phrases. However, once they are sung with the main words and set to music and become a complete song, they show distinct emotions and become an inseparable and organic part of the entire song. components.

If these supporting words and phrases are removed, it will not only greatly weaken the expressiveness of the song and make the song lose its luster, but also often destroy the integrity of the song structure, and even make it impossible to sing at all.

In order to distinguish the main words, these foil words are collectively called "line words", and they are often enclosed in brackets when writing scores. The tune that lines the lyrics is called "lining tune".

Because the lining words and lining tunes have different positions in the song and have different relationships with the preceding and following sentences, their functions are also different. For example, the lining words and melody in Lesson 1 of Volume 4 of the Junior High School Music Textbook "Ten Sings in the Border Area" can play a role in connecting and transitioning.

It fully demonstrates that during the Anti-Japanese War, the military and civilians in the liberated areas worked together and responded to Chairman Mao's call to be self-reliant, have adequate food and clothing, vigorously open up wasteland and cultivate land, carry out large-scale production, and contribute to the Anti-Japanese War. By cleverly arranging words and accents, the scene and enthusiasm of military and civilian mass production are displayed.

Another example is Lesson 5 of Volume 2 of the junior high school textbook "The Little Road in Hometown": 1=D3 slowly and affectionately. In the above example, if the singing ends after singing the last line of the main lyrics, the audience will have a feeling of plummeting. Through the two measures of eight-beat backing, the rhythm will gradually slow down and become lighter, and the whole song will end affectionately. In this way, even if the song ends perfectly, it brings "me" back to my childhood. The small road in my hometown, the little flowers on the roadside, and my mother's words are still fresh in my mind like yesterday's events. Indeed, if the lining words and lining tone are used properly, singing will definitely achieve twice the result with half the effort.