install older macOS guest directly from Apple-provided disk image

Yosemite, High Sierra, and Sierra are no longer available via the Mac App Store mechanism. Instead, their respective Apple support pages provide a disk image download, which contains a package installer, which, when run, installs the "Install Mac OS X" app that Parallels requires to set up a macOS guest.

However, the package will not run on the host OS if it predates the release of the hardware it's running on, making it impossible to extract the "Install Mac OS X" app, making it impossible for Parallels to install the older macOS version as a guest OS.

It would be very helpful to those who need to run older software, or troubleshoot older systems, to be able to easily install an older macOS as a guest.

(The workaround I found, after very considerable trial and error, is to install a current macOS as a guest in Parallels; within there, the installer package can be run, regardless of the age of the host hardware.)