(HTTP language/coding): Improve last change.

man/url.texi

@@ -319,10 +319,14 @@ Default is one hour.
 HTTP allows clients to express preferences for the language and
 encoding of documents which servers may honour.  For each of these
 variables, the value is a string; it can specify a single choice, or
-it can be a comma-separated list in descending order of preference.
-Each element can be followed by @samp{;q=@var{priority}} to specify
-its preference level; e.g., for @code{url-mime-language-string},
-@w{@code{"de, en-gb;q=0.8, en;q=0.7"}}.
+it can be a comma-separated list.
+
+Normally this list ordered by descending preference.  However, each
+element can be followed by @samp{;q=@var{priority}} to specify its
+preference level, a decimal number from 0 to 1; e.g., for
+@code{url-mime-language-string}, @w{@code{"de, en-gb;q=0.8,
+en;q=0.7"}}.  An element that has no @samp{;q} specification has
+preference level 1.
 
 @defopt url-mime-charset-string
 @cindex character sets