[range.range] Fix example to clarify who/what is being specialized for/with/on what.

Author: Dawn Perchik

source/ranges.tex

@@ -873,12 +873,18 @@
 
 \pnum
 \begin{example}
-Specializations of class template \tcode{subrange}\iref{range.subrange}
-model \libconcept{safe_range}.
-\tcode{subrange} specializes \tcode{enable_safe_range} to \tcode{true}, and
-\tcode{subrange}'s iterators
--- since they are ``borrowed'' from some other range --
-do not have validity tied to the lifetime of a \tcode{subrange} object.
+Each specialization \tcode{S} of class template \tcode{subrange}\iref{range.subrange}
+models \libconcept{safe_range} because
+\begin{itemize}
+\item
+\tcode{enable_safe_range<S>} is specialized
+to have the value \tcode{true}, and
+
+\item
+\tcode{S}'s iterators
+do not have validity tied to the lifetime of an \tcode{S} object
+because they are ``borrowed'' from some other range.
+\end{itemize}
 \end{example}
 \end{itemdescr}