Merge pull request #6085 from Rdatatable/fix6079

link measure from the list of valid measure.vars values

man/melt.data.table.Rd

@@ -27,7 +27,7 @@ non-measure columns will be assigned to it. If integer, must be positive; see De
     \item{ When missing, \code{measure.vars} will become all columns outside \code{id.vars}. }
     \item{ Vector can be \code{integer} (implying column numbers) or \code{character} (column names). }
     \item{ \code{list} is a generalization of the vector version -- each element of the list (which should be \code{integer} or \code{character} as above) will become a \code{melt}ed column. }
-    \item{ Pattern-based column matching can be achieved with the regular expression-based \code{\link{patterns}} syntax; multiple patterns will produce multiple columns. }
+    \item{ Pattern-based column matching can be achieved with the regular expression-based \code{\link{patterns}} (regex without capture groups; matching column names are used in the \code{variable.name} output column), or \code{\link{measure}} (regex with capture groups; each capture group becomes an output column). }
   }
 
     For convenience/clarity in the case of multiple \code{melt}ed columns, resulting column names can be supplied as names to the elements \code{measure.vars} (in the \code{list} and \code{patterns} usages). See also \code{Examples}. }