$float =~ m/
            \A             # beggining of string
            \d{0,$max_lhs} # 0 to $max_lhs digits
            (?=            # non capturing grouping
            \.             # decimal point
            \d{1,$max_rhs} # 1 to $max_rhs digits
            )?             # grouping is optional
            \z             # end of string
           /xms;