-results in the value of that variable for the case @var{ncases} before
-the current one. In case-selection procedures, @code{LAG} results in
-the value of the variable for the last case selected. Results in
-system-missing (for numeric variables) or blanks (for string
-variables) for the first case or before any cases are selected.
+yields the value of that variable for the case @var{n} before the
+current one. Results in system-missing (for numeric variables) or
+blanks (for string variables) for the first @var{n} cases.
+
+@code{LAG} obtains values from the cases that become the new active file
+after a procedure executes. Thus, @code{LAG} will not return values
+from cases dropped by transformations such as @cmd{SELECT IF}, and
+transformations like @cmd{COMPUTE} that modify data will change the
+values returned by @code{LAG}. These are both the case whether these
+transformations precede or follow the use of @code{LAG}.
+
+If @code{LAG} is used before @cmd{TEMPORARY}, then the values it returns
+are those in cases just before @cmd{TEMPORARY}. @code{LAG} may not be
+used after @cmd{TEMPORARY}.