WMS Request Question - possible BBOX bug.

[Tweedy, Scott]

Leave it to other users to bring something up.  I'm feeding information to
MapServer through a PHP form (for demonstration purposes) and a user tried
this combination for the BBOX -89,50,-78.35x,60.0xxxx (my regular expression
didn't pick up the letters properly).

The WMS request after this is correct and it produced the proper image, is
this a bug in MapServer?  I don't know of any projection system that accepts
letters for a bounding box.  Why didn't the letters crash MapServer or
simply produce no image?

I'm using MapServer 4.3:
MapServer version 4.3 OUTPUT=PNG OUTPUT=JPEG OUTPUT=WBMP OUTPUT=PDF
OUTPUT=SWF SUPPORTS=PROJ SUPPORTS=FREETYPE SUPPORTS=WMS_SERVER
SUPPORTS=WMS_CLIENT SUPPORTS=WFS_SERVER SUPPORTS=WFS_CLIENT INPUT=OGR
INPUT=GDAL INPUT=SHAPEFILE

here's the actual request format:
SERVERNAME?version=1.1.1&Layers=Mineral%20Deposits%20of%20Canada&BBOX=-89,50
,-78.35x,60.0xxxx&request=getMap

Thanks in advance once again.
st