I think you can't find anything because Perl is smart enough to "Do What You Mean" (tm).

#!/usr/bin/perl
use strict;
use warnings;
use diagnostics;

my ($number1, $number2, $number3) = <DATA>;

my $number = 5.13E-04;
my $other = "5.13E-04";

print "sum 1 = ", $number + $other;
print "\n";
print "sum 2 = ", $number1 + $number2 + $number3;

__DATA__
5.12E-04
5.12E+04
1
[download]

Results:

sum 1 = 0.001026
sum 2 = 51201.000512
[download]

Cheers,

Brent