#A.19.SOURCE-SET-SPACE-SUBSTRATE:4.7 - Conditional fields stay conditional

Preface node heading:a-19-source-set-space-substrate-4-7-conditional-fields-stay-conditional:23965

#What this page is

This is generated FPF reference text from the specification preface or supporting sections. It helps interpret FPF; it is not FPF Reference product documentation.

#Methodology

Use it to understand how the specification wants to be read, then return to a route, pattern, or work packet for active work. Cite generated IDs only when the wording changes the task decision.

#Content

Use SourceSetComposition only when the line genuinely consumes several declared source sets.

When composition is active:

• SourceSetFamily still names the primary family the line is anchored on;
• SourceSetComposition names the additional declared source-set families or the explicit composed-source posture that widens that primary family;
• the composition field does not replace the primary family, and it does not silently retitle the whole line as one different source kind.

Use DerivedViewKind only when one derived view is materially active and the reader must be able to recover that derivation.

Use BasePaletteRef only when a derived tradition or palette view would otherwise hide the recoverable base palette.

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Last Updated: 2026-06-08 — upstream FPF commit 093d30e8 (github.com/ailev/FPF)