External References - Allowed?

hi,

let's see if i can explain this...

i have a top assembly - called

AB

Assembly AB contains 2 sub-assemblies - called

A

and

B

Sub-assembly A contains a part called A1

Sub-assembly B contains a part called B1

i would like to EDIT sub-assembly B and assemble/mate part B1 referencing a feature of A1.

out of the box, SolidWorks 2016 won't let me do this.

i have tried different settings in the EXTERNAL REFERENCES area of the SYSTEM OPTIONS menu.

no worky.

any thoughts on this?

can i create external references willy-nilly like i used to be able to do in (horrors) Pro-Engineer?

thanks in advance.

fred