首先要了解下定界符
php可以使用
<?php
echo <<<EOT
this is body
this is body as well
EOT
;
这种方式来输出大段文字，其中EOT就是定界符，定界符有分为开始定界符和结束定界符，定界符可以是任何内容，只要保证开始定界符和结束定界符一致就行，比如
<?php
echo <<<AAA
this is body
this is body as well
AAA
;
这就是heredoc的写法，heredoc中的变量会被解析成具体的值
<?php
$a = 'this is string';
echo <<<AAA
this is body
this is body as well
$a
AAA
;
// output
this is body
this is body as well
this is string
如果希望内容不被解析，可以在开始定界符的两边加上单引号'EOT'
<?php
$a = 'this is string';
echo <<<'AAA'
this is body
this is body as well
$a
AAA
;
// output
this is body
this is body as well
$a
这就是nowdoc的写法
