Enumerations for _Chem_comp_descriptor.Type (An open enumeration)
`INCHI` | 'InChi descriptor'
`INCHI_CHARGE` | 'InChi descriptor- charge layer'
`INCHI_FIXEDH` | 'InChi descriptor- fixed hydrogren layer'
`INCHI_ISOTOPE` | 'InChi descriptor- isotopic layer'
`INCHI_MAIN` | 'InChi descriptor- main layer'
`INCHI_MAIN_CONNECT` | 'InChi descriptor- main layer - atom connection sub-layer'
`INCHI_MAIN_FORMULA` | 'InChi descriptor- main layer - chemical formula sub-layer'
`INCHI_MAIN_HATOM` | 'InChi descriptor- main layer - hydrogen atom sub-layer'
`INCHI_RECONNECT` | 'InChi descriptor- reconnected layer'
`INCHI_STEREO` | 'InChi descriptor- stereochemical layer'
`SMILES` | 'SMILES descriptor'
`SMILES_CANNONICAL` | deprecated
`SMILES_CANONICAL` | 'Canonical SMILES descriptor'