Can GetPCCell check for an exact exterior cell (like for instance "0,0" or "-3,8"), or can it only check for the naming (like just "Bitter Coast").

getpccell works for cell name (such as "bitter coast"), getpos will give you your coordinates. usage is like this -

player->getpos x

or

mynpc->getpos y

http://www.uesp.net/wiki/Tes3Mod:GetPos

http://www.uesp.net/wiki/Tes3Mod:GetPCCell

Naming (partial, so GetPCCell "Balmora" will be true both for "Balmora" and "Balmora, Caius Cosades House".
You can simulate cell coordinates check though, as a cell is 8192 units. Something like this should work

begin celltestScript; we want tho check if we are for instance in cell -3, 8float templong x1long y1set temp to ( player->GetPos X )  ; unitsset temp to ( ( temp / 8192 ) + 0.5 ) ; cellsset x1 to temp  ; truncatedset temp to ( player->GetPos Y )set temp to ( ( temp / 8192 ) + 0.5 )set y1 to tempif ( x1 == -3 )	if ( y1 == 8 )		MessageBox "You are in cell %g, %g" x1 y1	endifendifend