ms44, variable substitution, mapfile EXTENT object attr

[Matt Pettis]

Hi,
 
I am trying to write a mapfile that will use javascript to dynamically sent EXTENT values to a .map file via POST parms.  Concretely, when I select a county in MN from a dropdown, I want to send the appropriate values for the EXTENT bbox so that the selected county is rendered in it's specific bbox.
 
The beginning of my mapfile looks like this:
---
MAP
 IMAGETYPE      PNG
 EXTENT       %xmin% "%ymin%" "%xmax%" "%ymax%"
 SIZE        880 660
 ...
---
 
the url i issue is:
http://localhost/cgi-bin/mapserv.exe?map=C%3A%5Cms4w%5CApache%5Chtdocs%5Ctest_postgis2%5CDynSQL_ByCounty%5Cmap.map&map_web_imagepath=C%3A%5Cms4w%5CApache%5Chtdocs%5Ctmp%5C&mode=map&xmin=439430.71875&ymin=4959166&xmax=486045.78125&ymax=5010473.5&coid=27
 
 
the error i get is:
 getDouble(): Symbol definition error. Parsing error near (%):(line 7) 
 
line 7 is the EXTENT line.
 
So, my questions are:
1.  Does MapServer support variable substitition for extent values?  If so, what am i doing wrong?  If not, how do I dynamically set the extent for dynamically selected polygons with different bboxes?
 
2.  Is there a better way to set the bbox rather than send it precalculated values in a GET?  It seems natural that I should be able to leave the EXTENT line off and a default of the smallest bounding box that works for the returned geometry would be returned as a default.
 
tia,
Matt