php nowDoc and HereDoc

<?php
//heredoc 注意 名称之前不能有任何输出 相当于双引号定界符
$id=2;
$username='queen';
$email='123@.qq.com';
$str="<table border='1' width='80%' bgcolor=\"pink\">
<tr>
<td>编号</td>
<td>用户名</td>
<td>邮箱</td>
</tr>
<tr>
<td>1</td>
<td>liuan</td>
<td>[e-mail]</td>
</tr>
<tr>
<td>{$id}</td>
<td>{$username}</td>
<td>{$email}</td>
</tr>
</table>";
echo $str;
//通过heredoc的写法
$str=<<<EOF
    this is a test
    <h1 align='center'>Hello world<small>power by king </small></h1>


EOF;
echo $str;
//table>tr*2>td{x}*3
$str=<<<TABLE
<table border='1' width='80%' bgcolor="gold">
<tr>
<td>编号</td>
<td>用户名</td>
<td>邮箱</td>
</tr>
<tr>
<td>1</td>
<td>liuan</td>
<td>[e-mail]</td>
</tr>
<tr>
<td>{$id}</td>
<td>{$username}</td>
<td>{$email}</td>
</tr>
</table>
TABLE;
echo $str;
echo "<hr/>";
$str=<<<"test"
<h1>这样写<small>也行</small> </h1>
test;
echo "$str";
echo "<hr/>";
#下面是nowdoc 相当于单引号
#注意，中间不可以有输出

$str=<<<'EOD'
<h1>this is test</h1>

用户名:{$username}
EOD;
echo "$str";