Nearly 14 months since its launch, the editorial experimentation at Vox Media's general-interest news site Vox.com continues.

Last week Vox.com rolled out an embeddable version of its card stacks so that other sites can feature these flash-card-like explainers within their own articles, like they might a YouTube video.

"We think of card stacks as very core not just to our editorial mission but to the soul of Vox. They are the clearest manifestation of what we are trying to do differently," said Vox.com Editor-in-Chief and Co-Founder Ezra Klein.

"We want to have our storytelling across a variety of formats where the audience is to see it," said Vox.com Executive Editor and Co-Founder Matthew Yglesias.

Originally card stacks were designed as annotations to Vox articles. A person could be reading a story about ISIS, not know the terrorist group's history and open a card stack to get some background before returning to the story. But then the card stacks evolved from being a sidebar to the main content for some people.

"What we saw in the user behavior was that people were really seeking these card stacks out and trying to read them basically front to back," Mr. Klein said. Within a couple of months, the Vox.com team "realized people were not primarily using these as reference materials for articles. They were using these as guides to a topic they wanted to learn more about."

That spurred a multi-month revamp of the card stacks. "We overhauled the entire editorial approach to them, making them much more readable front and back [and] really changing the way we approached their internal continuity," Mr. Klein. Capping that process was making the card stacks embeddable outside of Vox.com, which has branding and business benefits for the year-old site.

For example, card stacks have become a way for Vox.com to get high school and college students to check out its site. Educators have directed their classes to read Vox.com's card stacks to bone up on class topics like the protests in Ferguson, Missouri, over the police shooting of Michael Brown, said Mr. Klein.

"One of the biggest responses that we've gotten to our card stacks is actually from universities and professors. I love that they are seeing our topical resources as an additional teaching tool," said Vox.com co-founder Melissa Bell, who was recently promoted to VP of growth and analytics for the site's parent company Vox Media. Now that card stacks can be embedded, educators can include them on any class sites they maintain, which can help grow the site's audience and potentially its advertiser base.

It may pique advertisers' interests to know that brands can piggyback these card stacks. "We have the capacity to target display ads to the card stacks to advertisers that want to reach like-minded audiences off our platform," Ms. Bell said.

That could help assuage marketers' concerns about advertising with Vox.com since card stacks can be more brand-friendly than some of the news site's normal coverage. Horizon Media's media director Natalie Orozco said that while her clients have bought ads on other Vox Media sites including The Verge, Eater and SB Nation, they have yet to advertise on Vox.com because its content is "more news heavy" and brands are often wary of being associated with breaking news stories that often cover sensitive or negative topics. Those advertiser hesitations are in spite of the site's audience growth.

Since its official launch in April 2014, Vox.com has grown in many respects. Its U.S. web traffic has grown 469% since that launch month to total 12.8 million U.S. unique visitors in April 2015, according to comScore. It's roughly doubled in headcount to around 44 employees. But the scope of the site's content formats have grown as well, such as the videos it has produced.

"In terms of our video strategy, we started with a couple assumptions that I think have paid off well. One thing is that we were really focused on having a social video strategy rather than an inventory video strategy," Mr. Klein said. By that he means not creating videos just to dress up a text-heavy article and bring in some lucrative video ad dollars.

"We were very clear with our team from the outset that we're going to make fewer but better [videos], and we're going to judge the success of that team not on how well a video did on our article pages but how well it did on native platforms like YouTube," Mr. Klein said, adding that he didn't want the videos to be a summary of the content already on Vox.com.

That video strategy seems to be working on YouTube, in particular. Of the 164 videos Vox.com has posted to its YouTube channel as of May 28, the average video has notched 271,007 views, according to publicly available data pulled by Ad Age directly from YouTube. Of the 103 videos Vox.com has posted to its Facebook page, the average video has received 77,020 views, per data pulled by Ad Age directly from Facebook.

Here are two charts breaking down the view counts and lengths for each of the videos Vox.com has posted to its YouTube and Facebook channels. Both charts' views axes have been capped at lower numbers because some videos had larger-than-normal viewerships that would make it hard to see most videos' view counts with normal chart formatting. You can hover over each entry to see the actual figures.

It's unclear why there is such a big viewership gap between Vox.com's YouTube and Facebook videos. It may have to do with the way YouTube and Facebook measure views; YouTube counts a view once a video has played for roughly 30 seconds whereas Facebook counts it after having played for three seconds. Or it may have to do with the length of these videos. Based on the data collected by Ad Age, Vox.com's average YouTube videos runs for four minutes and 33 seconds while its average Facebook video is only one minute and three seconds long. Mr. Klein dismissed the idea that Vox.com is programming differently for YouTube versus Facebook.

"A lot of the videos that have gone up on YouTube are the same videos that have gone up on Facebook and vice versa," Mr. Klein said. He added that the video length difference may be symptomatic of Vox.com using YouTube to develop its video strategy early on and then later porting that strategy to Facebook as well.

However comparing the upload dates and lengths of the videos Vox.com has posted to its YouTube and Facebook channels indicates there is some differentiation going on. Of the 164 videos Vox.com has posted to YouTube, only 12 were posted to Facebook on the same day and at the same length. The remaining 152 YouTube videos either were posted to Facebook on a different day or at a different length or were never posted to Facebook. (Scroll to the bottom of this article for a head-to-head look at the videos Vox.com has posted to its YouTube and Facebook channels).

More recently Vox.com has been developing its short-form article strategy. Some months ago Mr. Yglesias created a section on the site called Xpress for shorter stories. Then earlier this month Vox.com hired Fusion's then social media director Margarita Noriega to be its short-form editor and oversee the section's development.

Instead of a dedicated short-form section, Vox.com could have opted to intersperse shorter posts among its medium-length stories and longform features. But it recognized that shorter article formats require a certain expertise, in the same way the explainer, graphic and video formats do (each of which also have their own specialized editors). And the site wanted to invest in that expertise "because a lot of content is best short," Mr. Klein said. That fits with Vox.com's broader editorial strategy of figuring out the best way to tell each individual story as opposed to forcing its content to adhere to traditional formats.

"We really want to deliver news in the ways that readers want. Sometimes readers want the news in three sentences and sometimes they want it in 3,000 words. And it depends on if they have the time to get on a pair of headphones and watch a video. And it depends on if they have the time to read a very longform feature. We think about formats a lot because we're thinking about what are the best ways to service the readers," said Ms. Bell.