disabled when the header "Content-length" is set.
#One could argue that any output handler could change the size of the
#response, so this exception for zlib.output_compression is an
#inconsistency. However, zlib.output_compression is presented as a
#performance setting, whose value should have no effect on the
#correctness of the scripts. This was not the case. Setting the
#header "content-length" and enabling zlib.output_compression was
#a recipe for infringing section 4.4 of RFC 2616.
Máté Kocsis