Use proposals to explore alternatives for a given area within your model. Every model starts with an initial proposal called "master". You can create your entire design in the master or you can create proposals for various alternative designs. You cannot delete or rename the master proposal.
You can also start a new proposal from another proposal. Keep in mind that changes in the parent proposal (including the master) are not automatically included in child proposals. You must manually merge changes into each proposal. For more information, see To merge proposals.