Built-In "Accessible" Theme

Hello,

One of the built-in themes is labeled as "Accessible". What makes this built-in theme accessible when compared to other built-in themes?
I thought that there might be some settings in this theme that would make it accessible without additional work by the developer. For example, I expected to see all slide titles set as Heading level 1 by default. However, this is not the case. 

As I understand it, there are built-in enhancements that make the default "Accessible Feedback Layers" and the "Accessible Player" accessible. Are there enhancements built in to the "Accessible" theme that are not visually apparent? 

Thank you,

Dan