When the Armv8-M Architecture Reference Manual was released in 2016, it introduced a new writing style for Arm documentation: rules-based writing. This Armv8-M architecture manual describes the behavior of the processing element as a set of individual rules. Each rule is assigned a unique and permanent identifier, for example R_BSHJ. The rules are complemented with explanatory information, which also has identifiers, for example I_PRTD.

Rules-based writing brings several benefits to readers and users of the architecture. It gives a clear and unambiguous way to refer to specific behaviors in the architecture, which remain valid across revisions of the manuals. It also gives clear separation between architectural rules and explanatory content.

Arm is now working on moving the A-profile documentation to rules-based writing. As a preview, Arm is releasing sample manuals in the new style:

These documents are provided for review and feedback; use the email alias referenced in the documents to provide feedback. The existing manuals remain the primary reference.