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Please note that for maximum robustness you should express any regular expression in IFs as /regexp contents/ or qr{regexp contents}, NOT as "regexp contents": the doublequoted variant only works for very simple patterns. The perl equivalency sign for strings 'eq' will not function as a regex in these items.
The substituted values are inserted into the expression in double quotes. In versions 2.0.4 and above, the special characters @%$"` are backslash-escaped to ensure that Perl does not interpret them when the expression is evaluated. In version 2.0.4 and above, purely numeric values are inserted unquoted as they are; before they were inserted double-quoted like strings.
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