This macro evaluates an expression and returns the result VARIABLE. This should usually be used only in extension @xref{besCOMMAND} commands and not in @xref{besFUNCTION}. The result is @b{NOT} duplicated and @b{NOT} mortalized and therefore the command modifying the VARIABLE may happen to modify a BASIC variable.
This should not be done! There are other ways to modify the value of a variable.