Provide defaults for all properties in the spec. In XRC schema, make
all properties optional. The previously required ones are annotated as
"important" (read: should be set unless you know what you're doing), but
aren't enforced.
The code already behaved like this, so this just synchronizes the
specification with the reality.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75043 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
1662725c75
