[unord.req] Spell out the behaviour of cbegin/cend, remove ambiguous note

Author: tkoeppe

source/containers.tex

@@ -2746,8 +2746,9 @@
 \tcode{b.cbegin(n)}
 &   \tcode{const_local_iterator}
 &   \requires \tcode{n} shall be in the range \tcode{[0, b.bucket_count())}.
-    Note: \tcode{[b.cbegin(n), b.cend(n))} is a valid range containing
-    all of the elements in the $\texttt{n}^{\textrm{ th}}$ bucket.%
+    \tcode{b.cbegin(n)} returns an iterator referring to the
+    first element in the bucket. If the bucket is empty, then
+    \tcode{b.cbegin(n) == b.cend(n)}.%
     \indextext{unordered associative containers!\idxcode{cbegin}}%
     \indextext{\idxcode{cbegin}!unordered associative containers}%
 &   Constant
@@ -2756,6 +2757,8 @@
 \tcode{b.cend(n)}
 &   \tcode{const_local_iterator}
 &   \requires \tcode{n} shall be in the range \tcode{[0, b.bucket_count())}.%
+    \tcode{b.cend(n)} returns an iterator which is the past-the-end
+    value for the bucket.%
     \indextext{unordered associative containers!\idxcode{cend}}%
     \indextext{\idxcode{cend}!unordered associative containers}%
 &   Constant