On a web page the arrangement might be sequential or hierarchical. Visual arrangement also involves spatial orientation within a field, as in left and right, up and down.
Arrangement also governs the organization of the text itself.
Headings and other textual elements ought to be distinguished from dissimilar elements. In any communication some parts are more important than others and should therefore receive more attention. This prominence or intensity of expression is what we mean by emphasis. Emphasis at a higher level includes use of headers to organize the content of the page and give clues to the structure of the content of the page and the site. Strategies for clarity help the receiver decode the message and to understand it quickly and completely.