h5bp/server-configs — pull request #68 by Matt-Stevens (2012-05-10 12:18:06+00:00)
Title: NGINX – IE5 and IE6 GZIP

IE5 and IE6 are always detected by NGINX, I'm guessing for keepalive reasons. You can see this in the “ngx_http_process_user_agent” function in “http/ngx_http_request.c”.

When deciding whether or not to disable GZIP, NGINX looks for the “msie6” string before moving on to executing regular expressions.