Title: How to Browse Delphi's VCL Source Code
If you have a Delphi version that comes with the source code (YES! some Delphi versions include the full VCL / RTL source code), you can easily browse through it! Here's how:
While in the Code Editor (editing your program's source code) press the CTRL key.
Keep the CTRL pressed while moving the mouse over a Delphi's class name, keyword, method, procedure, etc...
For example: drop a TButton on a form. Hold the CTRL key, move your mouse over the "TButton" word in the form's interface declaration. The TButton gets underlined.
Click the underlined word.
Magic: The "stdctrls" unit is displayed in the Code editor. Pointer placed on the implementation of the TButton class.
Yes, what you are now looking at is the Delphi source code.
Note: while editing your own code, use the same technique to jump to, for example, a variable declaration - CTRL+Click it to see when and how it was declared.
Here are some more source code navigation tricks.