TCP Mapping -- Shrinking the Window

The tcpmapping document is silent with respect to shrinking a window after it has been advertised.

This behavior is inconsistent with window-based flow control (the window's edge should never be moved to the left). However, because the specification is silent, there is confusion as to what should happen if this behavior occurs.

Should the tcpmapping document include wording similar to that in the relevant sections of RFC 1122 that makes it clear that the window may be advanced only to the right?