Change Default Search engine button on browser Source code

If you have a search engine and you want to ask the browser to set it to the default search engine, how do you do it?

For example, as you can see on http://www.dogpile.com/

"Add dogpile to your browser"

All that dogpile button does is return an OpenSearch description file. What to do with that is up to the browser; Most will add the described search engine to their list of shortcut search engines.