What do you mean by "one song outside" or "two songs outside"?

When the same poet publishes two poems in newspapers and periodicals at the same time, for the convenience of readers, the editor puts the two poems together and marks them beside the title of the first poem (except one) to remind readers that there is another poem by the author. If three songs are published at the same time, it can be called "two songs are outside", and so on. Generally speaking, after the author writes the main text, there are occasional works. At the same time, an external song is related to the main work to some extent, which supplements what the author has not written and perfects the author's inner expression, so it is called an external song.