add function signature and behavior comment

selfdrive/car/fw_query_definitions.py

@@ -97,10 +97,16 @@ class FwQueryConfig:
   non_essential_ecus: dict[capnp.lib.capnp._EnumModule, list[str]] = field(default_factory=dict)
   # Ecus added for data collection, not to be fingerprinted on
   extra_ecus: list[tuple[capnp.lib.capnp._EnumModule, int, int | None]] = field(default_factory=list)
+
   # Function a brand can implement to provide better fuzzy matching. Takes in FW versions,
   # returns set of candidates. Only will match if one candidate is returned
   match_fw_to_car_fuzzy: Callable[[LiveFwVersions, OfflineFwVersions], set[str]] | None = None
 
+  # Alternate matching function that takes FW versions and the VIN and returns a set of matches.
+  # If there are conflicts with the union of all other matching functions (exact, fuzzy, or custom fuzzy),
+  # then the result from this custom one takes precedence.
+  match_fw_to_car_custom: Callable[[LiveFwVersions, str, OfflineFwVersions], set[str]] | None = None
+
   def __post_init__(self):
     for i in range(len(self.requests)):
       if self.requests[i].auxiliary: