Hi,
Additional types of Extended Community attributes may be defined, where the intention is to have those attributes passed transparently (i.e., without being changed by the PE routers) from CE to CE. This would allow CE administrators to implement additional route filtering, beyond that which is done by the PEs. This additional filtering would not require coordination with the SP.
Reference : RFC 4364
Actually, they telling you that they're not going to strip them from your routes. IT mean's that you would need to match on your communities on the other side and then make routing decisions based on whatever community you were matching on.
Best regards,
kazim