All that stuff is called content. The meaning of content is more than the sum of its parts. The way they are positioned, and their order, all make a difference in the meaning. Notice that the content of this page is all mixed together. You can have pictures next to text, or in-between text, and you can have text on pictures.
Web sites can be like collages of different forms of content.
The rules that govern meaning take into account the different forms of content, the way they are positioned, and the way they are ordered. You can make a set of rules by coming up with a list of the criteria something must have in order to convey a particular meaning. For example, let's say you wanted to make a set of rules that govern all Web sites that have to do with Star Wars. Now you could boot up your browser, look at any random Web site, and compare the characteristics of that site against the rule set above. Of course, you've probably spotted a problem here.