= Known incompatibilities with Smarty 2 =
== PHP Version ==
Smarty 3 is PHP 5 only. It will not work with PHP 4.

== {php} Tag ==
The {php} tag is disabled by default. The use of {php} tags is
decripated. It can be enabled with $smarty->allow_php_tag=true.

But if you scatter PHP code which belogs together into several
{php} tags it may not work any longer.

== Delimiters and whitespace ==
Delimiters surrounded by whitespace are no longer treated as Smarty tags.
Therefore, { foo } will not compile as a tag, you must use {foo}. This change
Makes Javascript/CSS easier to work with, eliminating the need for {literal}.
This can be disabled by setting $smarty->auto_literal = false;

== Unquoted Strings ==
Smarty 2 was a bit more forgiving (and ambiguous) when it comes to unquoted strings 
in parameters. Smarty3 is more restrictive. You can still pass strings without quotes 
so long as they contain no special characters. (anything outside of A-Za-z0-9_) 

For example filename strings must be quoted
<source lang="smarty">
{include file='path/foo.tpl'}
</source>

== Extending the Smarty class ==
Smarty 3 makes use of the __construct method for initialization. If you are extending 
the Smarty class its constructor is not called implicitly if the your child class defines 
also constructor. In order to run Smarty's constructor, a call to parent::__construct() 
within your child constructor is required. 

<source lang="php">
class MySmarty extends Smarty {
   function __construct() {
       parent::__construct();
    
       // your initialization code goes here

   }
}
</source>

== Autoloader ==
Smarty 3 does register its own autoloader with spl_autoload_register. If your code has 
an existing __autoload function then this function must be explicitly registered on 
the __autoload stack. See http://us3.php.net/manual/en/function.spl-autoload-register.php 
for further details.

== Plugin Filenames ==
Smarty 3 optionally supports the PHP spl_autoloader. The autoloader requires filenames 
to be lower case. Because of this, Smarty plugin file names must also be lowercase. 
In Smarty 2, mixed case file names did work.

== Scope of Special Smarty Variables ==
In Smarty 2 the special Smarty variables $smarty.section... and $smarty.foreach... 
had global scope. If you had loops with same name in subtemplates you could accidentally 
overwrite values of parent template.

In Smarty 3 these special Smarty variable have only local scope in the template which 
is defining the loop. If you need their value in a subtemplate you have to pass them 
as parameter.
<source lang="smarty">
{include file='path/foo.tpl' index=$smarty.section.foo.index}
</source>

== SMARTY_RESOURCE_CHAR_SET ==
Smarty 3 sets the constant SMARTY_RESOURCE_CHAR_SET to utf-8 as default template charset. 
This is now used also on modifiers like escape as default charset. If your templates use 
other charsets make sure that you define the constant accordingly. Otherwise you may get 
not output.