What were you trying to do that didn't work?

From the example in https://libvirt.org/formatdomain.html#hard-drives-floppy-disks-cdroms we can see that the disk image can have dataStore and backingStore with dataStore. But when we use the full xml, it will have error:
XML error: The <source> of <dataStore> can't have another nested <dataStore> or <backingStore> element

Please provide the package NVR for which the bug is seen:

libvirt-10.10.0-8.el10_0.x86_64
qemu-kvm-9.1.0-15.el10.x86_64

How reproducible is this bug?:

100%

Steps to reproduce

1. Can refer to the steps in https://issues.redhat.com/browse/RHEL-85319 to create the images if necessary.
2. Edit the guest xml with the following disk xml:

    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2' cache='none' io='native' discard='unmap'/>
      <source file='/var/lib/libvirt/images/datastore.qcow2'>
       <dataStore type='file'>
        <format type='raw'/>
        <source file='/var/lib/libvirt/images/datastore_2'/>
      </dataStore>
    </source>
    <backingStore type='file'>
      <format type='qcow2'/>
      <source file='/var/lib/libvirt/images/base-with-data-file.qcow'>
        <dataStore type='file'>
          <format type='raw'/>
          <source file='/var/lib/libvirt/images/datastore_1'/>
  </dataStore>
      </source>
    </backingStore>
    <target dev='vdb' bus='virtio'/>
    <address type='pci' domain='0x0000' bus='0x05' slot='0x00' function='0x0'/>
    </disk>

3. Will get the error:
# virsh edit avocado-vt-vm1
error: XML error: The <source> of <dataStore> can't have another nested <dataStore> or <backingStore> element
Failed. Try again? [y,n,i,f,?]:

Expected results

Can edit and start the guest.

Actual results

Can't edit guest and start guest failed.