EXTENT versus SIZE in Mapserver

I am working with 3 vectorial layers and these layers are bigger than the research area (EXTENT) I have defined the extent area to be 35 30 95 60 (lower left corner, upper right corner) dd of lat/long. Still the mapserver was rendering data from outside the extent area


It took me a while to understand the reason. The problem is with the SIZE parameter, in the above pic the size was 800 500 so the area was a bit out of the EXTENT and Mapserver will not have a problem to render any data outside the EXTENT so that the image gets the proper size.

Changing the SIZE to 800 400 I get a prefect image