Function insert_section 

pub fn insert_section(
    page: &PageView,
    after: Option<usize>,
    text: &str,
    new_id: NewId<'_>,
) -> Vec<EventSpec>

Inserts a section with text after the section at after (None: at the front). When no order fits between the neighbours the page is renumbered first, one CAS field.set order per section.