Left      Right      Description and pseudocode
===============================================================
Any       undef      check whether Any is undefined
                     like: !defined Any

Any       non-ref    string equality
                     like: Any eq Any

Any       Regexp     pattern match
                     like: Any =~ /Regexp/

Any       CODE       sub passed Any returns true
                     like: CODE->(Any)

Any       ARRAY      smartmatch each ARRAY element[3]
                     like: grep { Any ~~ $_ } ARRAY

Any       object     call `MATCH` method on Object,
                     or invoke ~~ overloading on Object,
                     or die

Any       other      die