The class cnstr is a nice little speedup, but since the introduction of RegisteredField, the speedup it gives is much smaller. So I would like to remove it and use std::string for the keys of the fields. Now I have made a "typedef std::string cnstr" which can by enabled by setting the macro NO_CNSTR. Setting it will currently break binary compatibility. I will set it on monday. This will allow us to slowly remove all use of cnstr by replacing all mention of it by std::string.