This image shows three views: the post and its two subposts, one audio file and one image.
The blue square is audio.jpg, which is included with the default theme and can be used whenever audio is uploaded. Notice that the audio subpost has the icon floating to the left of the description. This is done by attachment.php, which has been programmed to use a different CSS class when the icon has a width less than 128px.
The attached image is actually much wider than the theme and would look horrible in some browsers if we didn’t give it an explicit width attribute. The new template tag that displays the image link can be given a set of numbers to constrain the image while maintaining its proportions. Clicking on this constrained image take the visitor to the file’s URL so they can view it outside of the confines of the theme.