2.91.3 (unstable):

* Element: Remove a redundant nullptr check
  (Renu Tyagi) Bug #757515

* Use scoped enums (enum class) instead of unscoped enums
* Document: Test for nullptr in a constructor
* DomParser: Make operator bool() explicit
  (Kjell Ahlstedt)

* The ABI and API are not identical to libxml++ 2.91.2.
  There may be more changes in ABI and/or API before the first stable
  libxml++-3.0 release.