The doc is rather inconsistent, at the start of perlop is the following table:

Customary  Generic        Meaning        Interpolates
        ''       q{}          Literal             no
        ""      qq{}          Literal             yes
        ``      qx{}          Command             yes*
                qw{}         Word list            no
        //       m{}       Pattern match          yes*
                qr{}          Pattern             yes*
                 s{}{}      Substitution          yes*
                tr{}{}    Transliteration         no (but see below)
        <<EOF                 here-doc            yes*
    

        * unless the delimiter is ''.
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Note: it says single quotes do not offer interpolation. So, as in most holy books, it depends on which part of perlop you (carefully) read.