Convert Text To HTML

I need a simple PHP script that converts indented text into properly formated HTML, by performing the following 2 actions: 1.- Converts text blocks preceded and followed by blank lines into an h4 HTML header 2.- Converts tab indentations into HTML blockquotes I have attached 2 files. The first "source.txt" contains an example of source text and "target.txt" contains the result of the conversion. The script has to provide me with a textarea in which I can paste the source text and a "Preview" button. Clicking that "Preview" button and without reloading the whole page (AJAX will be used instead) the bottom of the page must show me how the resulting text looks like and show me a textarea where I can copy the resulting HTML code. [login to view URL] contains the h4 and blockquotes styles than must be used in the preview.