Comments

Single line

# Shell style comment

// C++ style comment

• Single-line comments apply up to the end of the line or the current block of PHP code, whichever comes first.
• They cannot be used to comment an entire line of code, if the code contains a closing PHP tag (even if there's no additional code after the closing PHP tag).
• There may be other instances in which single-line comments don't work as expected (non-intuitive), especially where there's a mix of html and PHP code.
• They're not truly end-of-line comments as in C++, Perl, Java, etc.

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

Multiple lines

/* C style comment */

/* This comment spans
   multiple lines */

• C style comments cannot be nested.