Implementation is not finished yet! But have a look at the source of PHPTAL/PreFilter.php:

There's base abstract class for prefilters. Previously you had to implement interface, now you'll have to extend the class. This change allows me to add new ways of filtering in the future without any breaking changes in the interface.

The class has methods like filterDOM($node), filter($source) — you just override which ones you want. You can override all of them at once if you need, all will be called.

DOM version lets you edit PHPTAL DOM nodes after they've been parsed and edit exactly what PHPTAL "sees".

There's also filterDOMFragment($node) method. I plan to add phptal:filter="name_of_the_filter" attribute, which will let you apply filters selectively, e.g. (this is not implemented yet)

 <ul phptal:filter="remove_whitespace">
  <li>IE hates newlines in lists</li>
 <script phptal:filter="minify_javascript">

I've replaced PHPTAL→setPreFilter($filter) with PHPTAL→addPreFilter ($filter, $name = null). Yes, this means you can have any number of filters without workarounds (finally! :)

I wonder if there should be separate method for adding named prefilters for use with phptal:filter only? (e.g. you might want to make JS minification prefilter available, but you don't want to minify entire file). Currently I expect this to be handled within filter, i.e. filter would implement filterDOMFragment() only, and have filterDOM() do nothing.

Is that easy to use? Powerful enough? What do you think?

Suggested improvements

link prototype

The API looks ok to me, just one thing, since it's not a runtime operation (in the sense that a php file is generated for the template), I think it'll be great if it used something along the lines of Zend_Loader_PluginLoader.

Which basically when setup with paths and class prefixes is able to find "plugins" in several folders. This would allow to have a set of default filters in PHPTAL distribution but override them and create new ones easily just by placing the class files in a directory, not needing to register them manually at runtime, which once the template is compiled, is of no use.

So – phptal:filter="remove_whitespace" – would automatically try to include and instantiate a class for that filter.

While – PHPTAL->addPreFilter("remove_whitespace") – would just store the name for when compiling the template and instantiate the class then.