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DerivedFrom

property DerivedFrom: string read write;

Example​

procedure ScriptEvent(var Value: variant);
begin
  if Response <> nil then
  begin
    { Only for a private contract that still defines this obsolete field. }
    Response.SetCustomHeader('Derived-From', 'example-source-2');
    Value := Response.CustomHeaders.Values['Derived-From'];
  end;
end;

Usage​

DerivedFrom reads or writes a transient legacy Derived-From value that automatic response sending clears before transmission.

Additional Technical Info​

DerivedFrom maps to FResponseInfo.CustomHeaders.Values['Derived-From']. Like Allow, this is the wrong collection for the bridge's automatic-send sequence: immediately before sending, MoveCookiesAndCustomHeaders clears that Indy list and replaces it with WebBroker CustomHeaders.

An assignment can therefore be read back during the action but is normally absent from the wire. If a private compatibility contract genuinely requires the old field, use SetCustomHeader as shown in the example.

Derived-From appeared in obsolete HTTP/1.1 material and is not a current HTTP semantic field. Velox does not interpret it as data lineage, content negotiation, cache validation or an audit relationship. Modern designs should carry provenance in a documented application representation/field rather than assume generic clients understand this value.

No syntax, URI, version or control-character validation occurs. Do not put internal paths, identifiers or untrusted text into a public field without a specific disclosure/encoding policy. An empty direct value removes only the transient entry. Test Response for nil.

External references

Created 2026-07-15