+ (when decode-break-reason
+ ;; If we've already read some characters on when the invalid
+ ;; code sequence is detected, we return immediately. The
+ ;; handling of the error is deferred until the next call
+ ;; (where this check will be false). This allows establishing
+ ;; high-level handlers for decode errors (for example
+ ;; automatically resyncing in Lisp comments).
+ (when (plusp total-copied)
+ (return-from ,in-function total-copied))