wxPPIxregexplain.pl

ppi_dumper -W -C foo.pl
...
  PPI::Statement
    PPI::Token::Symbol  	'$html'
    PPI::Token::Operator  	'.='
    PPI::Token::HereDoc  	'<<END'
    PPI::Token::Structure  	';'
...

Now that you know the name (heredoc), you can search for it,  [perldoc://heredoc] heredoc -> perlop#<<EOF