The first key feature uniting various formats of parliamentary debate in the US is their spontaneity. The resolutions alternate each round. They are announced, then participants are given 20 minutes of preparation time known as "prep". APDA is somewhat of an exception in the respect, with "loose link" rounds allowing the affirmative to run a case of their choosing, dealing with virtually any topic. The second key feature of parli is a ban on quoted evidence. Debaters may not bring in any material that was not prepared in the 20 minutes of preparation time and consult it during the round. APDA, Worlds and high school parli debate styles tend to take a more lay-friendly approach to debate, ensuring that debates are easy to understand no matter the audience member's expertise of the resolution. NPDA is more diverse, with some teams engaging in a more academic and specific-knowledge style borrowed from Policy debate. Resolutions typically focus on current events, though the entrance of the Kritik to NPDA, and, to a lesser extent, to some high school circuits, introduced a philosophical element to parli.