If you based any code off the "Selections" programmer's example, you may be using the selection.selectionModels() function to get a list of models to restrict selections to. That function is going away with the next release. You should use the chimera.openModels.list() function instead as explained in the revised example now on the Chimera web site. Using the openModels.list() function will work in 1.1951 and prior releases as well as our next release which should be out next week. At one point, it had been our intent to allow users to designate a set of models to restrict selections to, which was the raison d'etre for the selectionModels() function. The implementation of an interface designating such models never materialized and over time the whole mechanism just seemed to be unnecessary, so we are dropping the idea and the corresponding API baggage. I apologize for any inconvenience. Eric Pettersen UCSF Computer Grpahics Lab pett@cgl.ucsf.edu