SQL Developer code 'Advanced Format' versus 'Custom Format' Preferences -> Code Editor -> Format -> Advanced Format
versus
Preferences -> Code Editor -> Format -> Advanced Format -> Custom Format

As I understand, both are alternative options to (re)format code in SQL Developer, where Advanced Format bases on .xml and Custom Format bases on .prg.

It seems, that the Advanced Format is the default, which is used when pushing Ctrl+F7. 

How can I deactivate Advanced Format and activate Custom Format now?
The custom format allows you to augment what's available with GUI controls in the advanced formatter preferences page.

It uses arbori, a parse tree query language.

The developer, Vadim, discusses this in his blog here.

So you don't pick one or the other - both are in play when using the formatter.