PHP supports 'C', 'C++' and Unix shell-style comments. For example:

    echo "This is a test"; // This is a one-line c++ style comment
    /* This is a multi line comment
       yet another line of comment */
    echo "This is yet another test";
    echo "One Final Test"; # This is shell-style style comment

The "one-line" comment styles actually only comment to the end of the line or the current block of PHP code, whichever comes first.

<h1>This is an <?php # echo "simple";?> example.</h1>
<p>The header above will say 'This is an example'.

You should be careful not to nest 'C' style comments, which can happen when commenting out large blocks.

    echo "This is a test"; /* This comment will cause a problem */