Function replace_section 

pub fn replace_section(
    body: &str,
    heading: &str,
    content: &str,
) -> Result<SectionEdit, EditError>

Replace the addressed section’s content — everything under its heading line to the span end, deeper sub-sections included — with content. The heading line itself is preserved byte-for-byte (gaining a terminating newline only when unterminated content must follow it).