question: private void assertExtendSignaturePossible ( ) throws DSSException { final SignatureLevel signatureLevel = params . getSignatureLevel ( ) ; if ( XAdES_BASELINE_T . equals ( signatureLevel ) && ( xadesSignature . hasLTProfile ( ) || xadesSignature . hasLTAProfile ( ) ) ) { final String exceptionMessage = "Cannot extend signature. The signedData is already extended with [%s]." ; throw new DSSException ( String . format ( exceptionMessage , "XAdES LT" ) ) ; } }
target:  Checks if the extension is possible.