Incorrect highlighting with PHP 7.3 heredoc strings

[Riimu]

In PHP 7.3, heredoc (and nowdoc) strings can be terminated by the keyword at arbitrary indentation (which is used to strip indentation from previous lines).

For example, the following PHP code works in PHP7.3:

$string = <<<DELIMITER
  Foobar
  DELIMITER;
  
var_dump($string);

and outputs:

string(6) "Foobar"

However, as you can see, the highlighting grammar does not recognize the indented heredoc termination and it parses the var_dump as part of the heredoc string.

[d-luk]

Same problem here. A fix would be appreciated!