Hi
Not sure I understand properly!
When you say overrides which code are you overriding?
Most users want a reasonable simple screen. Basically the screen views are driven by the layouts which are like mini templates
Essentially the 'placeholders' { } are like macros or very simple plugins in the layout.Generally each line in a layout has its own css class associated with it. Many people use the custom css facility to customise.
You can make your own layouts as the screen design. The code generation phase in the default.php basically replaces the placeholders with relevant code. That is the layouts control the view on the screen.
What is confusing is the the layouts are multipart with header, footers sub headers and the main part. It is not necessarily clear which part is used when.
Do you perhaps have an example I could look at please.
Colin