How can I have use the same div ID multiple times on the same page?

Question

Okay so a problem I encounter a lot is that often times I want to use the same div ID several times on the same page. An example of this is when I'm creating table like designs.
Let's say for instance I create a div ID called 'product-container'. I want to use 'product-container' multiple times on the same page but if I do this it is improper XHTML and will throw errors in any XHTML validator (you are only allowed to use a div ID once on any XHTML page in order for it to be standards compliant).
Now the first option is that I could define 'product-container' in my CSS style sheet multiple times by doing something like this...
#product-container {
     width: 300px;
#product-container-2 {
     width: 300px;
#product-container-3 {
     width: 300px;
#product-container-4 {
     width: 300px;
What you will see there however is that it seems pointless to define the same ID numerous times over (just adding a number on the end) when each ID is the exact same thing and has the exact same attributes.
Now what I have noticed is that there are some sites out there who manage to have the same ID appear several times in the code but add a number to it just like above. The difference is that they only have one definition for 'product-cointainer' in their CSS document but in their actual XHTML code they have IDs for 'product-container' but with numbers on the end like 2,3,4,5, etc. It's almost as if JavaScript or some other code is automatically appending a number on the end of the ID so the validator won't consider the markup to be invalid, but yet it knows that it's using the same 'product-container' style that is contained in the CSS style sheet.
I hope I explained this correctly. I'm just hoping to find a way that I can put the same div ID on a page multiple times without having to define it over and over again in my CSS.
Any help is much appreciated!

Answer 1

Because it seems like by using a class you can't make this position as 
well as you can by using an ID. Am I wrong?
An ID name can be used only one time per page.  A class name can be used multiple times per page.
.product {
width: 300px;
text-align:left;
color: #FF0000
border: 2px solid #666;
Nancy O.
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