Improve manual on inheriting attributes

Expands first paragraph a bit
Adds a more comprehensive example

doc/manual/expressions/language-constructs.xml

@@ -61,7 +61,7 @@ evaluates to <literal>"foobar"</literal>.
 
 <simplesect><title>Inheriting attributes</title>
 
-<para>When defining a set it is often convenient to copy variables
+<para>When defining a set or in a let-expression it is often convenient to copy variables
 from the surrounding lexical scope (e.g., when you want to propagate
 attributes).  This can be shortened using the
 <literal>inherit</literal> keyword.  For instance,
@@ -72,7 +72,15 @@ let x = 123; in
   y = 456;
 }</programlisting>
 
-evaluates to <literal>{ x = 123; y = 456; }</literal>.  (Note that
+is equivalent to
+
+<programlisting>
+let x = 123; in
+{ x = x;
+  y = 456;
+}</programlisting>
+
+and both evaluate to <literal>{ x = 123; y = 456; }</literal>. (Note that
 this works because <varname>x</varname> is added to the lexical scope
 by the <literal>let</literal> construct.)  It is also possible to
 inherit attributes from another set.  For instance, in this fragment
@@ -101,6 +109,26 @@ variables from the surrounding scope (<varname>fetchurl</varname>
 <varname>libXaw</varname> (the X Athena Widgets) from the
 <varname>xlibs</varname> (X11 client-side libraries) set.</para>
 
+<para>
+Summarizing the fragment
+
+<programlisting>
+...
+inherit x y z;
+inherit (src-set) a b c;
+...</programlisting>
+
+is equivalent to
+
+<programlisting>
+...
+x = x; y = y; z = z;
+a = src-set.a; b = src-set.b; c = src-set.c;
+...</programlisting>
+
+when used while defining local variables in a let-expression or
+while defining a set.</para>
+
 </simplesect>