Heading
Headings get style “myHeading”, “mySubheading” and “mySubsubheading”. They were set to Outline Level “Level 1”, “Level 2” and “Level 3” respectively in the properties dialog of the style.

Subheading
I have defined a numbering style “myNumbering” with A on first level, A.I on second level and (a) on third level. This numbering style is referenced in a style:list-style-name attribute of the style “myHeading”.

Subheading
TOC is set up to use “Outline”. The current content is not updated, because LibreOffice introduces lists, but I do not want lists in this example.

Sub-Subheading
Dummy text

Sub-Subheading
Dummy Text

Heading
Dummy Test