If you are looking for Information about PSU Clementine, Go check their Wiki
Expert Types
From The re-PSUPedia
Expert classes are a big like FFXI's cross-classing system, in which you can play two classes at once
Requirements
in Both classes (Say for example HU and RA) you must have reached level XX (it's unconfirmed what it is, but is suspected to be mid-way to max level). You will then be given the option to play both at the same time.
Equipment
It isn't known how equips will work (Being able to use fat ion cannons and large swords doesn't seem to be very balanced) at this moment (The whole thing is rather vague right now).