RFC-RFCSTD-0002                                                   Section 2
Category: Standards Track                          Normative Requirements

2. Normative Requirements

2.1 Invariant Specification Requirement

Architecture RFCs MUST define at least one architectural invariant.

Each invariant MUST:

Requirement	Description	Verification
Be numbered	Format: Invariant N — Title	Check for numbered format
Use RFC 2119 keywords	MUST, MUST NOT, SHOULD, etc.	Search for keywords
Be falsifiable	Possible to determine if violated	Review for testability
Include rationale	Explain why invariant exists	Check for explanation

Architecture RFCs SHOULD define trust boundaries when the architecture involves:

Scenario	Trust Boundary Required
Multiple systems or components	SHOULD
Security-sensitive operations	MUST
Authorization decisions	MUST
Data flow between domains	SHOULD

Trust boundaries SHOULD be illustrated using Mermaid diagrams.

Architecture RFCs MUST include a Rationale section documenting:

Component	Requirement
Alternatives considered	At least one alternative
Why alternatives were rejected	Specific reasons
Invariant violations	Which invariants each alternative violated (if applicable)

Architecture RFCs SHOULD define component interfaces including:

Architecture RFCs MUST NOT contain:

Prohibited	Permitted Alternative
Working code in any programming language	Pseudocode for conceptual illustration
Configuration files (YAML, JSON, TOML, etc.)	Structural descriptions
Shell commands or scripts	Capability descriptions
Database schemas with actual field values	Schema concepts without values
API endpoint implementations	API contracts (input/output only)

Permitted in code blocks:

Permitted	Purpose
Mermaid diagrams	Visual representation
Format specifications (structure only)	Showing expected formats
Placeholder examples with obviously non-functional values	Illustrating concepts

Architecture RFCs MUST be organized as multi-file directories.

Rationale: Architecture RFCs are inherently complex and benefit from:

Architecture RFCs SHOULD include diagrams for:

All diagrams MUST use Mermaid syntax. All diagrams MUST be indexed in Appendix A.

End of Section 2 — RFC-RFCSTD-0002