It's hard to answer your question without any additional information. As I know, variable capExtent used in overLIB library and assigned to 'document' or 'window' object.
But overLIB haven't string like
Code:
f = capExtent.onmousemove.toString().match(/function[ ]+(\w*)\(/);
only
Code:
f = capExtent.onmousemove.toString();
As I know, this code returns source code of function, assigned to event 'onmousemove' and replaces some part of code with regular expressions. I think, there is no function assigned to event onmousemove or capExtent variable not assigned to any object.
Please, provide more information and I'll try to help you.