go to the Project menu and click the Project settings menu option;
use Ctrl+Alt+P shortcut.
The following dialog window will appear:
Generate filename using relative numbering (like in previous versions)
Select this option button if you want to generate file names using relative numbering: module_1, module_1_1 etc. (as in previous versions of Dr.Explain).
The preview area displays numbering style of all levels at once. Text of the currently selected level is black. Here you can click the text corresponding to the level you'd like to customize.