With regards to the rss-content, I thought that it would be possible to choose HTML due to the RSS feed generated from TUAW (
http://www.tuaw.com/rss.xml):
<?xml version="1.0" encoding="UTF-8"?>
<?xml-stylesheet href="http://feeds.tuaw.com/~d/styles/rss2full.xsl" type="text/xsl" media="screen"?><?xml-stylesheet href="http://feeds.tuaw.com/~d/styles/itemcontent.css" type="text/css" media="screen"?><rss xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:itunes="http://www.itunes.com/dtds/podcast-1.0.dtd" xmlns:feedburner="http://rssnamespace.org/feedburner/ext/1.0" version="2.0">
<channel>
<title>The Unofficial Apple Weblog (TUAW)</title>
<link>http://www.tuaw.com</link>
<description>The Unofficial Apple Weblog (TUAW)</description>
<image>
<url>http://www.tuaw.com/media/feedlogo.gif</url>
<title>The Unofficial Apple Weblog (TUAW)</title>
<link>http://www.tuaw.com</link>
</image>
<language>en-us</language>
<copyright>Copyright 2006 Weblogs, Inc. The contents of this feed are available for non-commercial use only.</copyright>
<generator>Blogsmith http://www.blogsmith.com/</generator><atom10:link xmlns:atom10="http://www.w3.org/2005/Atom" rel="self" href="http://www.tuaw.com/rss.xml" type="application/rss+xml" /><item><title><![CDATA[Weekend Review: this week's software]]></title><link>http://feeds.tuaw.com/weblogsinc/tuaw?m=280</link><guid isPermaLink="false">http://www.tuaw.com/2006/05/28/weekend-review-this-weeks-software/</guid><comments>http://www.tuaw.com/2006/05/28/weekend-review-this-weeks-software/#comments</comments><description><p>Filed under: <a href="http://www.tuaw.com/category/software/" rel="tag">Software</a>, <a href="http://www.tuaw.com/category/weekend-review/" rel="tag">Weekend Review</a></p><div id="pc622660"><img vspace="5" hspace="5" align="right" alt="" src="http://www.tuaw.com/media/2006/05/BricksmithIcon.jpg" />Grab a cup of coffee and get your downloading mice ready ladies and gents; this week's software review is coming at you:<br /><br /><strong>Shareware<br /></strong>
<ul>
..... many more lines ....
As for the DIFF, I imagined getting the new HTML page with the background of the changed pieces highlighted. But I guess the link to an HTML-diff function would be fine. OTOH not something I really need, just thinking out loud.
