Contents 

1. Level 1 (5=)
1. 1. Level 1.1 (3=)
1. 1. 1. Level 1.1.1 (2=)
1. 2. Level 1.2 (3=)

1. Level 1 (5=)

1. 1. Level 1.1 (3=)

1. 1. 1. Level 1.1.1 (2=)

1. 2. Level 1.2 (3=)

The toc at the top is obtained via {{toc nr}}.

The highest level is always 1, independently of the actual size of the heading.
There is no need to have consecutive header sizes to have consecutive levels (see 5= => 3=).