Use the source xpix...
...or var_dump specific variables of the $modx object for inspection. There is way too much to see if you dump the entire object, though you can certainly keep raising your memory limit if you really want to go through the whole dump...
FWIW, just be aware that much is changing in 0.9.7 and many of the variables and functions that are not documented on the site or the wiki, are not intended for "public access"; virtualDir is one of them and why I brought this up. In other words, it’s not a good idea to depend on them in your components or you will have to refactor them if/when you decide to adopt one of the future releases.
There will be very clear API documentation for 0.9.7 and beyond to make it much easier to get started developing MODx add-ons and core extensions.