Perl has a mechanism for intermixing documentation with source code. While it’s expecting the beginning of a new statement, if the compiler encounters a line that begins with an equal sign and a word, like this

           =head1 Here There Be Pods!
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Then that text and all remaining text up through and including a line beginning with "=cut" will be ignored. The format of the intervening text is described in perlpod.

(Emphasis by me).

POD is only allowed at statement boundaries. This is probably because it's very confusing to have a huge piece of text between the beginning and the end of a statement, and thus would make reading the code much harder.