// function declaration with default value
function foo($bar = 'default value here'){ ... };
// function declaration with passing by reference
function foo(&$bar){ ... };

// This won't work in PHP < 5
function foo(&$bar = 'default value here'){ ... };

<?
// function declaration
function foo($bar = 'default value here') { ... };
// function calling
foo(); // valid call
foo(&$var); // this, however is consider deprecated in PHP >= 5
?>

<?
header("Location: http://www.domain.com");
header("Refresh: 5; http://www.domain.com"); // Redirect after 5 secs
?>

<?
// This won't work with Opera 7.54 or even earlier,
// or this never worked before in Opera up to 8.5
header("Location: http://www.domain.com/file01.php?do=something#anchorhere");
// No problem for this though
header("Refresh: 5; http://www.domain.com/file01.php?do=something#anchorhere");
// A method to overcome the problem in Opera
header("Refresh: 0; http://www.domain.com/file01.php?do=something#anchorhere");
?>

<?php
// Don't do this !
$value = urldecode($_GET['something']);
?>

<?php
$query = htmlspecialchars($_GET['query']);  
$query = str_replace('%2522', '', $query);  
$query = str_replace('%27', '', $query);  
$query = str_replace('%2527', '', $query);  
?>

<?php
// good 
str_replace('&amp;', '&', htmlspecialchars($_GET['redirect']);
// bad
htmlspecialchars(urldecode($_GET['redirect']));
?>

$name = 'Darren'; // This one's better
$name = "Darren";

echo '<a href="' . $url . '">' . $text . '</a>';
echo "<a href=\"$url\">$text</a>";
// You cannot do a \n with single quote
echo "\nThis is a new line\n";

<?php
session_start();
$_SESSION['test'] = "original";
$test = "modified";
echo $_SESSION['test'];
 
// this will output "modified" instead of "original"
?> 

<?php
$_SESSION['test'] = $something;
echo $_SESSION['test'];
 
// Point to the file in browser, with query append to the back:
// test.php?something=modified
// The string "modified" will be output
?>