BLOCK
           A syntactic construct consisting of a sequence of Perl statements
           that is delimited by braces.  The "if" and "while" statements are
           defined in terms of BLOCKs, for instance.  Sometimes we also say
           "block" to mean a lexical scope; that is, a sequence of statements
           that act like a "BLOCK", such as within an eval or a file, even
           though the statements aren’t delimited by braces.

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       expression
           Anything you can legally say in a spot where a "value" is
           required.  Typically composed of literals, variables, operators,
           functions, and "subroutine" calls, not necessarily in that order.