The standard is more like
# A union referencing different chardev backend configuration' info.
#
# @gnmouse: Send mouse data using the Genius protocol (since 2.0).
#
# Since: 1.4
##
but that format would require doucmenting all items. :(
You can leave this out of v2.
However, I'd be happy if you changed the documentation like this
@item -chardev msmouse,address@hidden
Forward events from QEMU's emulated mouse to the guest using the
Microsoft protocol. @option{msmouse} does not take any options.
@item -chardev gnmouse ,address@hidden
Forward events from QEMU's emulated mouse to the guest using the Genius
(Mouse Systems) protocol. @option{gnmouse} does not take any options.