我正在阅读 Google Analytics API 文档并注意到我以前从未见过/使用过的语法:
<script>
<?php
<<<HTML
  cxApi.setChosenVariation(
    $chosenVariation,             // The index of the variation shown to the visitor
    $experimentId                 // The id of the experiment the user has been exposed to
  );
HTML;
?>
</script>
做什么<<<HTML,这叫什么?