How do @PreAuthorize expressions access the current user and method arguments?

SpEL expressions in @PreAuthorize/@PostAuthorize have access to 'authentication' (the current Authentication object, e.g., authentication.name or authentication.principal) and to method parameters directly by name (e.g., #loanId for a parameter named loanId), as well as 'returnObject' in @PostAuthorize specifically for the method's return value.