Priority for extractors

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #107 
| License       | MIT
| Doc PR        | need to be written
somebody might do his own code to register extractors or otherwise change the container, and rely on the signature, so not having the default in the method sounds like a BC break to me. but your solution looks good to me.