Perl can handle arithmetic with strings, like '2x' and '3.e00.0.1.2y', consisting of a prefix that perl can recognize as a number followed by non-numeric stuff; for example 

% perl -wle 'print "2x" + "3.e00.0.1.2y"'
Argument "3.e00.0.1.2y" isn't numeric in addition (+) at -e line 1.
Argument "2x" isn't numeric in addition (+) at -e line 1.
5

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As far as I can tell1 this is an undocumented feature. Am I correct?

the lowliest monk

1I've scanned perlnumber and perlop for documentation, without success, but, admittedly, I haven't been able to come up with a good grepping strategy for this search.

In reply to Is '2x' + '3y' == 5 documented? by tlm

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