-Normally the aggregate file does not receive the documents from the
-active file, even if the aggregate file replaces the active file.
-Specify DOCUMENT to have the documents from the active file copied to
-the aggregate file.
-
-At least one aggregation variable must be specified. Specify a list of
-aggregation variables, an equals sign (@samp{=}), an aggregation
-function name (see the list below), and a list of source variables in
-parentheses. In addition, some aggregation functions expect additional
-arguments in the parentheses following the source variable names.
+Specify DOCUMENT to copy the documents from the active file into the
+aggregate file (@pxref{DOCUMENT}). Otherwise, the aggregate file will
+not contain any documents, even if the aggregate file replaces the
+active file.