jsdIStackFrame.pc semantics

The doc for jsdIStackFrame.pc reads:

Current program counter in this stack frame.

I have code like this:
--------
var req = new XMLHttpRequest();

req.onreadystatechange = function() {  // line 3
     if( req.readyState == 4) {
	        eval( req.responseText);  // line 5
     }
};
---------

When the eval() executes, within which line should I
expect the program counter for the caller? I expected
line 5, but it comes out on line 6. (Well the numerical
value is 4 since it comes out of pcToLine relative to
the start of the function).

So one model is that the PC is somehow at the end of
the function call:

		eval( req.responseText);  // line 5
---------------------------------------^
so it is just on the next line "barely".

Or there is just another "off-by-one" problem in my code,
not the first I guess ;-).

But I see one case where the PC points to the line
with the eval().

This is all with PCMAP_PRETTYPRINT output, which I guess
really means source-like text decompiled from bytecodes.

Thanks,
John.