ExcelBanter - Sort partially hidden data

I have a vba sort command that sorts four columns depending on the integer in the first column - very straightforward - but I was getting erratic results. In the application, some of the rows that are intended to be sorted were hidden, and it appears that those rows were not included in the sort. Is this normal? I changed to progam to 'unhide' the hidden rows before the sort and 'rehide' them again after the sort, and that appeared to solve the problem. I don't know if I solved the problem for sure or if I am on the wrong path even though it all seems to work. So I have two questions...

1) Do all of the rows in a vba-driven sort command have to be visible?
2) What about the basic Excel sort (I use that in other parts of the program).

It appears that those items don't have to be visible, but I cannot find any information that tells me the answer to that sort question either? I would appreciate it if someone could tell me the answer to those two questions. As always, thanks in advance.