Changing this set of allowed reaction specifications to be permissive means that certain cases that we know are not handled, like n005 to n008 are passed through without raising a warning, and the resulting error when importing the mechanism is not easy to diagnose as it no longer mentions the unsupported user input.

If I'm reading this correctly, it only supports the case where a single reaction id is given

this is correct. I didn’t see a way around replacing the warnings as I had assumed that correct cti conversion was most important.

Could you be more specific about n005 to n008?

Actually, there's always the option to still produce a warning while leaving the same in place. I added this as a separate commit, but can squash if necessary. As is, the conversion works, but produces a warning, i.e.

$ cti2yaml Mayur-ISSP.cti 
WARNING: Conversion of reaction specification 'rxn-SEI-comp' may not be supported

Edit: I ended up changing things, so this is obsolete

Take a look at some of the examples given here: https://cantera.org/tutorials/cti/phases.html#declaring-the-reactions

Admittedly, I've never seen this construct used in the wild, which is why I didn't worry about it for cti2yaml in the first place. But I've also the reaction selection used to pick just a single reaction, either.

@speth ... thanks! I think it's possible to add the conversion of n005 to n008 if it ever comes up. As it stands, the single reaction already came up, so I'd suggest to update the warning message and leave the import in place.

Edit: I added a separate error for anything containing to, and tweaked the warning message.

PS: found a better way by catching exceptions at a later point