Fix GH-1440: Mention that named arguments can't be used with empty()

Author: cmb69

language-snippets.ent

@@ -1647,7 +1647,8 @@ linkend="ini.open-basedir">open_basedir</link>.</para></note>'>
 
 <!ENTITY note.language-construct '<note xmlns="http://docbook.org/ns/docbook"><simpara>Because this is a
 language construct and not a function, it cannot be called using
-<link linkend="functions.variable-functions">variable functions</link>.</simpara>
+<link linkend="functions.variable-functions">variable functions</link>,
+or <link linkend="functions.named-arguments">named arguments</link>.</simpara>
 </note>'>
 
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