You can return anything you want when $1 equals "begin" or "end" but the practical use is to return "-" for line separators, if you want them.
If you want to ignore these iterations, thus returning nul string (implied return) then just delete those lines, or use the operator "isnum" and they will be skipped and ignored.
alias animal {
if ($1 isnum 1-5) return Cow $1 : echo Moo $1
if ($1 isnum 6-10) return Goat $1 : echo Goatnoise $1
}
