Mark J. Reed wrote:

>Where can I find documentation for standard library modules
>that are binaries rather than Ruby code?  For example, 
>Ruby comes with readline support, but as far as I can tell
>no documentation.  And since it's a .so I can't easily just look
>at the source (although I can always unpack the Ruby source distribution
>and dig that way).  I didn't see anything about it in my copy of the Pickaxe,
>either.
>
>Anyway, my specific question is this: how do I configure the readline history?
>If I just do this:
>
>	ruby -rreadline -e 'Readline.readline; Readline.readline'
>
>I have full editing capability on the input line, but no history;
>on the second one, I can't move up to the value I entered the
>first time.  But the same code executed in irb gives me access to
>the history (shared with the lines entered into irb itself).
>
>-Mark
>

If you're feeling brave you could read the ./ext/readline/readline.c 
file under the ruby source tree.
I often have to look in .c files to see what methods I have available to 
me. :)

Michael