Zend certified PHP/Magento developer

Multilevel list with custom increment symbols

I want to have a custom multilevel list that has leading incremental values as I specify them. So for example, for headings with the ‘Heading 1’ style, instead of

1 Heading

2 Heading

3 Heading

I want it to increment like

AB Heading

MN Heading

XY Heading

The ‘Heading 2’ should the again increment like a standard number, so

AB-1 Heading

AB-2 Heading

AB-3 Heading

I already tried everything I know but couldn’t find any solution to that. Is there any way to define the leading values? In Excel for example I can define a custom list that I can then use with the fill handle.