The draft currently says:
You may assume that you have everything necessary for RPM to function
and process your spec file (so of course RPM is present, along with
redhat-rpm-config and what is necessary for RPM to apply patches, unpack
archives, and run the shell scripts which make up the spec file
sections.) You should not assume any other packages are present, as RPM
dependencies and anything brought into the buildroot by the build system
may change over time.