Requirement Keywords

Normative

This page defines the requirement keywords used throughout the Chiisai HAL specification. It is referenced by every normative page.

The key words MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL in the normative parts of this specification are to be interpreted as described in RFC 2119.

Chiisai HAL uses three severity levels, which map directly onto the requirement clusters used in each module’s requirements page (see How to Read This Specification):

Keyword	Cluster	Meaning
MUST / MUST NOT	Mandatory	An absolute requirement of the specification. A conformant driver MUST satisfy every Mandatory requirement (see Conformance).
SHOULD / SHOULD NOT	Recommended	There may exist valid reasons in particular circumstances to ignore this, but the full implications must be understood and weighed before doing so.
MAY	Optional	Truly optional. An implementation may provide the feature; consumers must not assume its presence and must interoperate with implementations that omit it.

Note

Chiisai HAL deliberately uses the RFC 2119 vocabulary of the internet-standards community rather than a single shall form. This keeps the specification’s lineage close to open developer standards and signals its intent as an implementable contract, not a compliance document.