$ \Src\ k\ P\ V $ is a helper function giving the source set
according to the $ k $ flag. $ \Src $ is based on $ \Match $, the helper
function handling {\POSIX} regular expressions.
$ \Src\ k\ P\ V $ is a helper function giving the source set
according to the $ k $ flag. $ \Src $ is based on $ \Match $, the helper
function handling {\POSIX} regular expressions.