A particular SMILES may contain expressions that are not compliant with the official SMILES definitions, which should either be rejected or elicit a warning from a SMILES parser. For example, while C[N@@@H]C is not a syntactically proper SMILES, it is nevertheless accepted by the commercial toolkit ChemAxon 47 as well as CDK, which transform it to [#6;A][#7;AH1;@@@][#6;A]