n my previous article we've discovered the basics of PHP Streams and how powerful they were. In this tutorial we are going to use this power in the real world. First I'll show you how to build your custom filters and attach them to a stream, then we'll package our filters inside a document parser application.
He starts out by introducing the concept of filters in streams - bits of code that can be attached to the stream to perform operations on the data traveling through it. He includes a simple base64 encoding example with a fopen call to illustrate. He gets into more complex filtering by creating a Markdown filter capable of translating the incoming Markdown-formatted data into a document using the MarkdownExtra library. He also includes an example of another filter added on post-Markdown conversion, a Template filter using the RainTPL templating library.