The best known tags on the web are HTML tags with attributes, like <a href="URL"> for hyperlink, <p> for paragraph, and <b> or <font color="red""> for style.

A Content Object? is marked up with start and end tags, like this:

<a href="http://www.cmswiki.com">CMS Wiki</a>.

The enclosed content becomes a hyperlink when processed by the HTML parser in the browser.

The most powerful tags today are XML tags, where attributes associate Meta Data with a chunk of content.