in the batters box

[Little Jimmy]

Tonight at one of our high school clinics this came up. Another umpire and myself had a disagreement about what constitutes being in the batters box prior to the pitch. I said the feet can touch the line but no part of the foot could be over (outside the line).My fellow ump said feet could be over the line so long as any part of the foot was touching the line (for example, heal touching line with the majority of the foot outside). At the time of the disagreement I thought I was right(unless I'd lost my mind) but couldn't find it covered in the Fed book. I said I would look further when I was home.

I'm home. I found what I was looking for in the 2008 ASA book (7-3-A) but can't find anything corresponding in the Fed book. Am I missing something? If indeed it is not stated has it been addressed at any level? I need a Fed rule to hang my hat on.