Google may be the world’s largest, most widely-used search engine, but that’s not all it is. Over the years, through both homegrown projects and acquisitions, the search behemoth has become a bona fide publisher in its own right.

Not surprisingly, this has created tensions between Google and some of the publishers that rely on its SERPs which drive traffic to their websites.

If Google is a publisher, many argue, how can it play fair when it comes to those SERPs?

Some, of course, suggest that it can’t, and their arguments often have validity. But if an experiment that Google is running becomes more than an experiment, publishers may find themselves the most livid they’ve ever been.

While searching, an observant Google+ user noticed a new ‘Sources‘ content area that appeared to the right of search results, where AdWords ads normally appear. This ‘Sources‘ area contained information about his search terms, which included “twitter” and “rihanna.

In the case of the former, Google provided information about Twitter, including a brief description, as well as data about Twitter’s location and corporate status. In the case of the latter, Google displayed a considerable amount of information about recording artist Rihanna, including her birth date, height and loved ones. Google also included a photo and a list of some of her songs.

According to Search Engine Land’s Matt McGee, Google responded to questions about ‘Sources‘ with the standard “Google is constantly experimenting with new features“, so it’s not clear if and when ‘Sources‘ might roll out in a big way.

But if it does, you can be sure many publishers will not be happy. After all, if Google culls information it thinks a searcher might be looking for and displays that information within the SERPs themselves, one might reasonably expect searchers to click less on the search results.

Exacerbating the situation, of course, is the fact that Google appears to be gathering the content it displays in ‘Sources‘ from external websites, like Wikipedia. The same websites, of course, that appear next to ‘Sources‘ in the SERPs.

Even if ‘Sources‘ is little more than an experiment that goes nowhere, it hints at where Google is contemplating going, reminding publishers that the search engine that sends them so much traffic can be at the same time their best friend and worst enemy.