[syslinux] Can USB:syslinux install another USBstik?

[eas lab]

When a USBstiked-syslinux starts, it's the PC's firmare that's reading
the USB ?
But once the USBsyslinux takes over, has IT also got a USB driver?

Since my MotherBoard & 2009 Slackware built USBstik syslinux booter
were stolen I bought a <WinTel> laptop and USBextender to access my
old IDE & SATA disks.

With WinTel's new arrangement of not allowing the tail of the sda
to be free for linux installation: I've only installed linux to
some USBstiks.

The attempted reconstruction of the stolen original Slackware BootStik
seems valid, but it has no SATA of IDE to be tested with.
Apparent correctly specified sdXY give "block (0,0)" errors
and invalidly tried sdXY give "block (N,M)" errors - as expected ?

Can the syslinux [or a newer version] mount a USB root-partition?

== TIA.