[syslinux] Label scope

[Collins, Jeremy]

Thanks, that clarifies things for me. I recommend altering the wiki and
doc/menu.txt to reflect that as well. I can alter the wiki if needed,
but I don't have dev environment / git tree setup to make a patch for
the doc/menu.txt change. Maybe something like the below change, any
thoughts on wording?

-- old--
MENU BEGIN [tagname]
MENU END
Begin/end a submenu. The entries between MENU BEGIN and MENU END form a
submenu, which is marked with a > mark on the right hand of the screen.
Submenus inherit the properties of their	parent menus, but can
override them, and can thus have their own backgrounds, master
passwords, titles, timeouts, messages and so forth.

-- new --
MENU BEGIN [tagname]
MENU END
Begin/end a submenu. The entries between MENU BEGIN and MENU END form a
submenu, which is marked with a > mark on the right hand of the screen.
Submenus inherit the properties of their	parent menus, but can
override them, and can thus have their own backgrounds, master
passwords, titles, timeouts, messages and so forth. However CLI
elements, like labels, must remain unique in all menus and submenus.