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DerivedFrom

property DerivedFrom: string read;

Example​

procedure ScriptEvent(var Value: variant);
begin
  if Request <> nil then
    Value := Request.DerivedFrom
  else
    Value := '';
end;

Usage​

DerivedFrom returns the first unparsed legacy Derived-From header without applying resource-version or merge semantics.

Additional Technical Info​

DerivedFrom performs a case-insensitive Indy raw-header lookup for Derived-From and returns the first selected value as text. Velox does not remove quotes, validate a version tag, connect it to ContentVersion, retrieve a base representation or perform a merge/conflict check.

The field came from an obsolete HTTP/1.1 specification for describing the resource version from which an entity had been derived. It is not part of current HTTP semantics. Most requests will return empty, and a nonempty value has only application-defined meaning unless a governed legacy protocol explicitly specifies it.

Do not use this property as an optimistic-concurrency control by itself. Prefer current validators such as ETag/If-Match, or an explicit signed application version field with server-side state comparison. Treat the value as untrusted and length-bound it before diagnostics or persistence.

Multiple physical fields are not combined by this getter. Test Request for nil; reading the property has no versioning side effect.

External references

Created 2026-07-15