Here I am reading Paul Klee’s Pedagogical Sketchbook. This is the very beginning of the book. As you can see, it is about drawing lines. For example, Fig. 1 shows “An active line on a walk, moving freely, without goal. A walk for a walk’s sake. The mobility agent is a point, shifting its position forward.”
Keep in mind that those lines are both a representation of the content in Klee’s book and are actual lines in my drawing and on my paper, taking a walk for walk’s sake.