Blake is a technical communicator working on a user manual for a new software application. Blake starts by arranging the text in the manual on the left margin. This makes the text easier to read and helps to create a sense of order. Blake places all of the headings and subheadings in the center of the page. This helps to make the headings stand out and makes it easier for readers to find the information they're looking for. Which document design principle is Blake using?