With the following declarations:

chan c;
typedef struct{int  b;} B;
B d;

and a template with heading

Template(chan& b)

with one transition with the update d.b= req.b, where req is local of type B

the system
p := Template(c);
system  p;

results in the instantion of p with the update:
d.c= req.c

It looks like textual substitution that does not respect bindings.