Usually attributes are assigned just one class, but this doesn't mean that that's all you're allowed. In reality, you can assign as many classes as you like! For example:
<p class="text side">...</p>
Using these two classes together (separated by a space, not with a comma) means that the paragraph calls up the rules assigned to both text and side. If any rules overlap between the two classes then the class which is below the other in the CSS document will take precedence.
Two classes together 
Linear Mode
