The Introduction and the section on Exposing HTML features that do not directly map to accessibility API properties should be updated. I suggest that at least the following changes be made:

1. Introduce the APIs in a way that matches how they are are presented in the mapping tables, e.g., explain UIAExpress, and why MSAA+UIAExpress and MSAA+IA2 are columns to themselves. 

2. Explain what an "accessible" is.

3. Update the use of <header> as the example in Section 2. A few of the APIs now assign specific roles for this element.

There's undoubtedly more that could be done to improve these sections.