Code browsing has been a feature of the Delphi IDEs for some time. Press ctrl and click on an identifier and Delphi will take you to its declaration. But did you know this also works in the code completion popup? Try it:
File<ctrl-space>
The above will give you a list of all methods and variables that start with "File". Notice some you didn't now about? Want to know what they do? Just press ctrl and click on it and Delphi will take you to the declaration.
To see this and other cool stuff in action, see Steve's demo