Top-level section. This renders as "1 Introduction".
Nested section — renders as "1.1 Scope".
Renders as "1.2 Goals".
Renders as "1.2.1 Detail".
Renders as "2 Architecture".
Supplementary material.
Definitions of terms.
Dense reference layout.
More breathing room between sections.
No indentation; "1.1" still communicates depth.