Document the nil/default values of url-user-agent

* doc/misc/url.texi (Customization): Document the nil/default
values of url-user-agent.

1 files changed, 10 insertions, 4 deletions

diff --git a/doc/misc/url.texi b/doc/misc/url.texi
index 14a4c96cc47..0a96a5428b1 100644
--- a/doc/misc/url.texi
+++ b/doc/misc/url.texi
@@ -1337,10 +1337,16 @@ Connect directly.
 @end defopt
 
 @defopt url-user-agent
-The User Agent string used for sending HTTP/HTTPS requests.  The value
-should be a string or a function of no arguments that returns a
-string.  The default value is @w{@samp{User-Agent: @var{package-name}
-URL/Emacs}}, where @var{package-name} is the value of
+The User Agent string used for sending @acronym{HTTP}/@acronym{HTTPS}
+requests.  The value should be @code{nil}, which means that no
+@samo{User-Agent} header is generated, @code{default}, which means
+that a string is generated based on the setting of
+@code{url-privacy-leve}, a string or a function of no arguments that
+returns a string.
+
+The default is @code{default}, which means that the
+@w{@samp{User-Agent: @var{package-name} URL/Emacs}} string will be
+generated, where @var{package-name} is the value of
 @code{url-package-name} and its version, if they are non-@code{nil}.
 @end defopt