> When running rdoc on the Ruby 1.9.1 source folder, the output does not contain documentation for JSON. It was suggested to me that it could be because ext/.document has not been updated.

I've run into this too [the Gem class isn't there, BigDecimal tutorial
is missing].

Some possibly related issues:
http://rubyforge.org/tracker/index.php?func=detail&aid=26410&group_id=627&atid=2472
http://rubyforge.org/tracker/index.php?func=detail&aid=26444&group_id=627&atid=2472



> Also it is unclear to me what is STDLIB and what is Ruby Core. At the moment no documentation for the STDLIB in Ruby 1.9.1 is available anywhere (except maybe the Pragmatic Programmers Book).

The official documentation for the stdlib is currently only in the
rdocs, I believe.
=r