Use for editorial asides — the "italic pointer" that marks a detail without competing with the primary diagram grammar. Think marginalia: *"structure IS the index"*, *"no imports, no configuration"*.
- Italic + serif together signal "editorial voice" against the diagram's sans/mono body. Don't substitute italic sans or italic mono — the combination is load-bearing.
- Dashed path (`stroke-dasharray="4,3"`) distinguishes the callout leader from primary arrows (which are solid).
- Place callouts in margins (top-right, bottom-left). Never inside the active diagram area.
- Max 2 callouts per diagram. More becomes commentary, not signal.