Skip unhidden expressions?

[tueda]

Is there any way to make expressions be so to say "skip/local-to be unhidden"?

I want an arbitrary number of hidden expressions to be temporarily unhidden (for garbage collection of the hide file), but I want not to change the bracket indices of them. The garbage collection code should not know the names of the hidden expressions and their bracket information. The following code:

S x;
* Hide F with bracketing.
L F = 1+x;
B+ x;
.sort
Hide F;
.sort

* Clean up the hide file.
Unhide;
Skip;  * doesn't work!
.sort
Hide;
.sort

* Use the bracket of F. The expected answer is 1.
L G = F[x];
P;
.end

unfortunately gives

FORM 4.1 (Oct 13 2016, v4.1-20131025-246-gb13522f) 64-bits  Run: Fri Oct 14 21:06:54 2016

   G = 0;