PHP htmlspecialchars() function function converts some HTML special characters such as > < & " etc into &lt;, &gt;, &amp; and &quot; etc. Note the string parameter inside htmlspecialchars function should be quoted using single quote ' but not double quote ".

<?PHP
	$str='<table><tr><td>name<td>address</table>';
	echo $str;  //<table><tr><td>name<td>address</table>
	echo htmlspecialchars($str); 
	//&lt;table&gt;&lt;tr&gt;&lt;td&gt;name&lt;td&gt;address&lt;/table&gt;
	$str="<table><tr><td>name<td>address</table>";
	echo htmlspecialchars($str);  //Not converted
	//<table><tr><td>name<td>address</table>?>

htmlentities() function has similar usages.

<?PHP
	$str = 'test@gmail.com donated $4 dollars';
	echo htmlentities($str); //test@gmail.com &quot;donated $4 dollars
?>

PHP htmlspecialchars_decode() function is the opposite of htmlspecialchars().

<?PHP
	$str=htmlspecialchars('<table><tr><td>name<td>address</table>');
	echo $str; 
	//&lt;table&gt;&lt;tr&gt;&lt;td&gt;name&lt;td&gt;address&lt;/table&gt;
	$str2 = htmlspecialchars_decode($str);
	echo $str2;
	//<table><tr><td>name<td>address</table>
?>