The Downside of Markup: Examining the Harmful Effects of CSS and Javascript on Indexing Today’s Web

The continued development and maturation of advanced HTML features such as Cascading style sheets (css), js, and AJAX, as well as their widespread adoption by browsers, has enabled web pages to flourish with sophistication and interactivity. Unfortunately, this presents challenges to the web search community, as a web page’s representation in the browser (i.e., what users see) can diverge dramatically from its raw HTML content (i.e., what search engines index and retrieve). For example, interactive pages may contain content in regions that are not visible before a user action, such as focusing a tab, but which are nonetheless still contained within the raw HTML. We study this divergence by comparing raw HTML to its fully rendered form across a number of metrics spanning presentation, geometry, and content, using a large, representative sample of popular web pages. We find that a large divergence currently exists, and we show via a historical analysis that this divergence has grown more pronounced over the last decade. Finally, we conduct a retrieval experiment which shows that this divergence is already influencing web retrieval in a negative manner, and that we can improve performance by making use of properties that are only available via pages’ rendered forms. The general finding of our study is that continuing to index the web via simple HTML parsing will diminish the effectiveness of retrieval on the modern web.

This paper has been accepted for publication at CIKM’12, Maui, USA.