Facebook gave editors broad leeway in choosing topics for its Trending Topics system, according to internal documents obtained by The Guardian. The new documents show the precise instruction Facebook gave to its team of editors on how to choose which topics and publications to designate as Trending Topics.

Facebook has been racked by allegations that it systematically suppresses conservative news sources, based on the allegations of a former news editor reported by Gizmodo earlier this week. Facebook has denied any allegations of anti-conservative bias. As in earlier stories, the new documents refer specifically to the Trending Topics system, and don't affect the stories that appear in a user's central News Feed.

The new document's section on "importance" level tells a more complex story than simple anti-conservative bias. The document designates 10 outlets as particularly central, and instructs editors to only label a topic as a "National Story" or "Major Story" based on how many of those publications placed the news on their front page. The publications include The New York Times, BBC News, and USA Today as well as a number of conservative outlets like Fox News and The Wall Street Journal.

Still, editors could only choose between topics that had been surfaced by Facebook's trending algorithm, which monitors news websites as well as activity by Facebook users. In the event that a newsworthy event was not detected by the system, editors were instructed to flag the topic for the engineering team.

At the same time, the decision of which URL to assign to a given topic was left up to an individual editor's judgment. The document lists a number of criteria for making that decision, instructing editors to favor publications with exclusive sources, headlines that clearly convey the subject matter, and an approach that "is not biased or sensational."