Search results that incorporate structured data have new found importance to Google, and the company wants to help webpages improve search snippets by including the most important information people might be looking for.
For things like events, for example, somebody might be looking for location and start times. By using Google's new Data Highlighter tool, anyone using Google's Webmaster Tools can easily tag that information without having to enter any microdata into the page's HTML. That way, the critical information people are looking for will pop right up in the search results.
Data Highlighter Patterned on...Patterns
Before the Data Highlighter tool, the only way to tell Google's search engine about structured data was by fiddling with the HTML. Now that data can be highlighted with the new tagging tool right from the Webmaster Tools' Optimization link in the left sidebar. Under that link is the Data Hightlighter.
Once in the Data Highlighter, simply input the URL of a page with structured data. Once that page appears, highlight the important fields and then label them. From there, Data Highlighter will look for similar data on other pages, and highlight them as well. Those pages can then be reviewed and corrected, and once published, Google will apply that pattern to the entire site, no matter how big it is.
That highlighted data will show up right in the search results snippets. It's only available in English right now, and only for things like events. Google will add more data types and languages in the months ahead.
Highlight and tag data to be shown in rich search snippets.
Knowledge Graph Included, Pages Behind Sign In Forms Left Out
Data Highlighter will eventually work with more types of data, and Google's search engine will be able to include any of that data from pages it can see. Search snippets will include this highlighted data -- products like the Knowledge Graph also will. However, for pages that are hidden -- like those behind a sign in form -- the Data Highlighter won't work.
As noted above, Data Highlighter can teach Google about similar pages within a given website, but those pages have to display the data in a consistent manner. Data Highlighter works with what are called page sets, and they are collections of pages that have the similar data displayed and are organized so their URLs follow a simple pattern.
Any pages that already have structured data nested within the HTML will not be included in this. Data Highlighter will ignore those already marked pages, but will still teach Google about the pages that aren't marked.
However a website organizes its pages, different page sets can be set up for each segment. If the organization of the pages or their URLs changes significantly. It might be a good idea to go back and delete the original page sets and enter in the new structure in Data Highlighter.
Let us know in the comments if you like the rich snippets feature on the search results page or if you think it is more valuable to just show more results overall.