Bad use of "its" replaceed with a rephrase. I noticed this flaw thanks to the

Debian bug report http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=443734

docs/curl.1

@@ -106,8 +106,8 @@ file instead of overwriting it. If the file doesn't exist, it will be created.
 If this option is used twice, the second one will disable append mode again.
 .IP "-A/--user-agent <agent string>"
 (HTTP) Specify the User-Agent string to send to the HTTP server. Some badly
-done CGIs fail if its not set to "Mozilla/4.0".  To encode blanks in the
-string, surround the string with single quote marks.  This can also be set
+done CGIs fail if this field isn't set to "Mozilla/4.0". To encode blanks in
+the string, surround the string with single quote marks. This can also be set
 with the \fI-H/--header\fP option of course.
 
 If this option is set more than once, the last one will be the one that's