When converting InCHI to canonical SMILES using Indigo, I will occasionally get an output SMILES string like this:
C[Si](C)C |^1:1|
What does the "|^1:1|" part mean? I can't find this explained anywhere in either SMILES grammar documentation, nor Indigo documentation, although other chemical software seem to accept it as a valid SMILES string. Any ideas on the meaning of this annotation?