Omit confusing sentence about undefined behavior.
Explain how the type descriptor is encoded in HDF5.
Set all NX keywords in special font.
Revise Sect IV:
- avoid the term "NeXus dictionary" (to avoid confusion with our description
  of base classes as dictionaries, and just to save a term that is not
  reused elsewhere)
- clearly distinguish "base class" and "base class name"
- give a simpler explanation of what a base class is
- use "data field" as a term that comprises simple data types and subgroups
- say explicitly: there is no mechanism to mark keywords as obligatory
- mention that NeXus does not specify the rank of data fields
Move remarks about changing base classes or submitting application definitions to the Governance section.
More text moved to governance section.
Revise beginning of Sect V: what's an application definition.
Say it once, but concisely.