Structure
While participating in a class activity, I reviewed Aviary's HTML content. I was very pleased to find that the entire site was based solely on semantic content markup and not presentational content markup.
The above image displays the semantic content markup by including the h1 and h2 tags.
Semantic markup is much more important for web sites to possess than it is to have presentational content markup because a site needs to be able to be transcoded. Sites should display the same structure and design on any device. Semantic content markup has become more popular with the introduction of smart phones and other hand held devices that have the internet on them.
"This semantic approach to web markup is a central concept underlying efficient web coding, information architecture, universal usability, search engine visibility, and maximum display flexibility." - Chapter 5 Web Style Guide 3rd Edition