plugin XEP-0131: Stanza Headers and Internet Metadata implementation: - SHIM is now supported and put in `msg_data["extra"]["headers"]`. - `Keywords` are converted from and to list of string in `msg_data["extra"]["keywords"]` field (if present in headers on message sending, values are merged). - Python minimal version upgraded to 3.11 due to use of `StrEnum`. rel 451

from typing import Optional

from twisted.words.xish import domish


class BaseError(Exception):
    namespace: str
    condition: str
    text: Optional[str]
    textLang: Optional[str]
    appCondition: Optional[domish.Element]

class StanzaError(BaseError):
    ...