The aggregation functions listed above exclude all user-missing values
from calculations. To include user-missing values, insert a period
-(@samp{.}) at the end of the function name. (e.g.@: @samp{SUM.}).
+(@samp{.}) at the end of the function name. (@i{e.g.}@: @samp{SUM.}).
(Be aware that specifying such a function as the last token on a line
will cause the period to be interpreted as the end of the command.)