You can inspect much of the internal structure of the class library and other data structures. This can be useful for research and debugging purposes.
Selecting the name of any method (e.g. play) and then the menu item Language>Look up Implementation
will open a window showing all implementations of that method and their arguments. Selecting one of those classes and methods (e.g. Sample:play) and typing enter will open the class definition at that method. Note that this only shows implementations, and does not indicate inheritance.
(see Keyboard Shortcuts)
Selecting any text (e.g. Window or asStream) and then the menu item Language>Look up References
will open a window showing all references to the selected text, i.e. each place it is used within the class library. Note that this will not find methods calls compiled with special byte codes like 'value'.
(see Keyboard Shortcuts)
SC has a graphical Class browser which will show all methods, arguments, subclasses, instance variables and class variables. Using the browser's buttons you can easily navigate to the class' superclass, subclasses, class source, method source, helpfile (if there is one), check references or implementation of methods.
Lots of information on server-related snooping can be found in the Server helpfile under "Information and debugging".
Some examples
When evaluating text in the interpreter, the variable 'this' always refers to the interpreter.