The ErrorCode typeclass under plutus-core/common/ErrorCode.hs assigns a positive number (Natural) to every error thrown by Plutus code. This package provides:

1. A Haddock catalogue of all errors (in-use or obsolete) and their codes src/Errors/Docs.hs.
2. A check for duplicates among error codes (implicitly achieved by haddock).
3. An executable plutus-errors-next to be used by Plutus developers to fetch a currently-unused error code (number).
4. An executable plutus-errors-bootstrap to initialize the codebase with automatically-generated ErrorCode instances.

Currently all errors among the project are placed into one big pile of error-codes. We will later use sub-groups of error-codes with specific ranges, e.g. (PIR : 0000 - 0100, PLC: 0100 - 0200, etc), which then would require to put into use the "wrapper-constructors" of our error-grouppings.

Run cabal haddock to generate the error catalogue.

After defining a brand-new Plutus-error and its ErrorCode instance, the developer must navigate to src/Errors.hs and update the list of all errors, so as the Haddock documentation can know about it and pick it up.

When an error was exposed to the public but it has become now obsolete (will never fire anymore) by removing (some of) its dataconstructors, then the developer should place move these obsolete data-constructors and their respective errorcodes to src/Errors.hs