Can someone help provide clarity on when to use an ID vs. a Class Attribute in your mark-up?

Saundra,

IDs and Classes achieve a similar goal, but in different ways. When you use them is defined by their individual intent, and then to some extent, personal preference. There are a lot of articles these days on the battle of using classes vs IDs, but ultimately, they both have their uses.

IDs are UNIQUE, and can only be on a given page once. By that, I mean individual IDs. You can have multiple elements with IDs on a single page, but the IDs must be different from one another, and any given element can only have one ID attached to it. For example, you can have two different paragraphs, and both paragraphs can have IDs, but they can't both have the ID of "paragraph". One would need to be something like "paragraph1", while the other was "paragraph2" (you, of course, would want to create more descriptive ID name than those, but this is just for simplicity's sake in this example).

Classes, on the other hand, ARE REUSABLE, and are meant to be applied to things that are more or less part of a group, or that will share styles across the page/site. In the example given above with the two paragraphs, if you were intending to style them the same way, you would give them both the same class (of, say, "paragraph") and then write styles for that class once, which would end up getting applied to everything that had that class attached to it.

Thus, you would generally use IDs on elements that are unique and intended to be styled uniquely (or targeted uniquely with JavaScript, for example), and you'd use classes on elements that were going to share styles with other elements across the page/site. As I stated, there are a plethora of articles out there from people who claim one is superior to the other, and you can find them very easily by doing a quick Google search of the question. Here, though, is a good article from Chris Coyier of CSS-Tricks (a very handy site) on the differences between IDs and Classes.

Erik