What characteristics distinguish an interactive story from another form of interactive media is subject to much debate. Interactivity and storytelling are both polysemic terms, and the phrase "interactive storytelling" does not inherently distinguish it from other kinds of storytelling, many of which are already interactive to some extent. Some of the literature associated with the term "interactive storytelling" is actually about transmedia storytelling, which is not a form of entertainment, but a marketing strategy for building a compelling brand across digital platforms. Varying levels of interactivity are a function of the "relatedness of transmitted messages with previous exchanges of information where sender and receiver roles become interchangeable." Storytelling, in this case, refers to the process of active creation and authoring rather than the final product and its passive reception. Interactive storytelling by this definition can entail any media that allows the user to generate several unique dramatic narratives. Though its final goal is a fully unauthored AI environment with a comprehensive human-level understanding of narrative construction (i.e., the Holodeck), projects that use branching stories and variable gates are considered experimental prototypes in the same genre.