:If this isn't mentioned in the article I might add it tomorrow. If you look at many of the Chinese paintings you'll notice that an area near the top, or sometimes side, is kind of without imagery and instead has calligraphy. This is intentional. Chinese painting was often both painting and poetry. Hence you'll fine many of the pre-Republican era painters were also poets because the two were often fused as one art. This is because, unlike with most Western languages, Chinese is ideographic. Therefore having a poem in a painting doesn't have to take up that much room, but sometimes it does. Long story short the calligraphy in Chinese paintings is usually a poem, as well as a demonstration of calligraphy in itself, and the poem is often by the painter. 

 :Another curiosity is that, somewhat less commonly, Chinese painters intentionally kept areas blank of calligraphy and painting. These blank spaces were filled by later painters of their school, sometimes over generations. This made the painting, in a sense, a "living art" which could change over time. Somewhat like how some folk songs are expanded or given additional verses over generation.(These analogies are a tad inelegant, I'm not a morning person)