For example, many painters may not draw anything in a corner of the paper when composing a composition, and barely drawing something also destroys the aesthetic feeling of the painting. But as a work, on the whole, the picture may have an "unbalanced" feeling, that is, poetry is used to fill the blank where there is nothing to draw, so that the picture is more suitable for the balanced beauty of vision.
So are other calligraphy works. In some places that appear "empty", seals are used to fill in the blanks, which increases the aesthetic feeling of the works.
From the above explanation, we can infer other meaning who fills in the blanks.