[Rd] reference class internals

[Norm Matloff]

I have a question about reference classes, which someone here
undoubtedly can answer immediately, saving me hours of wading through
indecipherable internal code. :-)  Thanks in advance.  

Reference class data is mutable, fine, but in what sense?  Is it really
physical,  or is it just a view given to the programmer?
 
If for instance I have vector as a field in a reference class, and I
change one element of the vector, is it really true that the change is
guaranteed to be made in-place, no copying, no memory reallocation etc?

Norm