How to check a request is subrequest or not?

Tue Jul 20 19:24:14 MSD 2010

Is these any variable just like the IS_SUBREQ Flag in apache?

http://httpd.apache.org/docs/2.2/mod/mod_rewrite.html

IS_SUBREQ
    Will contain the text "true" if the request currently being
processed is a sub-request, "false" otherwise. Sub-requests may be
generated by modules that need to resolve additional files or URIs in
order to complete their tasks.

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,110862,110872#msg-110872