This proposal would greatly increase the usefulness of rule sets by making it possible to insert a rule set anywhere in a list of rules. Specifically, the change would involve removing the "Mixins" keyword in favor of an approach that could apply a ruleset anywhere in a set of rules.  The proposed grammar will be "insert {ruleset}", as follows: * some rule * insert rule-set-1 * some other rule It will be possible to use an `insert` rule within a rule set. The "mixin" keyword would be denigrated, hence this change is non-compatible with previous versions of FSH. We validated this on the FHIR Shorthand call on 6/11/2020 and everyone was in favor of the proposed change.