In the fonts-conf(5) man page:
<ALIAS>
Alias elements provide a shorthand notation for the set of
common match operations needed to substitute one font family
for another. They contain a <family> element followed by
optional <prefer>, <accept> and <default> elements. Fonts
matching the <family> element are edited to prepend the list
of <prefer>ed families before the matching <family>, append
the <accept>able families after the matching <family> and
append the <default> families to the end of the family list.
No mention of the binding attribute, while it is used in various
config files under the /etc/fonts/conf.avail directory.