Document NIST SP 800-53 identifiers

[aj-stein-gsa]

User Story:

As a developer of OSCAL-based tools and content, in order to better understand how to analyze and process each group, control, control enhancement, and various part identifiers in different programming languages.

Goals:

When discussing FedRAMP use of the upstream NIST catalogs in this repository and how FedRAMP derives customized catalogs from resolving it with our profiles, we frequently receive developer feedback that it is unclear how the use of separators with -, _, . works for groups versus their controls, control enhancements, and the sub-parts of various kinds across SP 800-53 and SP 800-53A. It would be most helpful to document them in pseudo-code, and their relationship to one another, as implemented today for people to more confidently develop their own processing logic, whether it be Metaschema/Metapath-based or not.

Dependencies:

{Describe any previous issues or related work that must be completed to start or complete this issue.}

Acceptance Criteria

• All readme documentation affected by the changes in this issue have been updated.
• A Pull Request (PR) is submitted that fully addresses the goals of this User Story. This issue is referenced in the PR.
• The CI-CD build process runs without any reported errors on the PR. This can be confirmed by reviewing that all checks have passed in the PR.

{The items above are general acceptance criteria for all User Stories. Please describe anything else that must be completed for this issue to be considered resolved.}