@Section
   @Title { "@Tagged" }
   @Tag { tagged }
@Begin
@PP
The @@Tagged
tagged.sym @Index { @@Tagged symbol }
symbol takes a cross reference for its left parameter and an object, whose
value must be a juxtaposition of simple words, or several words, or an empty
object, for its right parameter.  It has the effect of attaching its
right parameter as an additional tag to the invocation denoted by its
left parameter, unless the right parameter is empty, in which case @@Tagged
does nothing.  The result of @@Tagged is always @@Null, which makes it
effectively invisible.
@End @Section