clarify new docs on attr value entity expansion
diff --git a/Doc/lib/libsgmllib.tex b/Doc/lib/libsgmllib.tex
index 592c191..cae6821 100644
--- a/Doc/lib/libsgmllib.tex
+++ b/Doc/lib/libsgmllib.tex
@@ -95,9 +95,16 @@
should be used to support semantic interpretation of the start tag.
The \var{attributes} argument is a list of \code{(\var{name},
\var{value})} pairs containing the attributes found inside the tag's
-\code{<>} brackets. The \var{name} has been translated to lower case.
+\code{<>} brackets.
+
+The \var{name} has been translated to lower case.
Double quotes and backslashes in the \var{value} have been interpreted,
-as well as known entity and character references.
+as well as known character references and known entity references
+terminated by a semicolon (normally, entity references can be terminated
+by any non-alphanumerical character, but this would break the very
+common case of \code{<A HREF="url?spam=1&eggs=2">} when \code{eggs}
+is a valid entity name).
+
For instance, for the tag \code{<A HREF="http://www.cwi.nl/">}, this
method would be called as \samp{unknown_starttag('a', [('href',
'http://www.cwi.nl/')])}. The base implementation simply calls