WhiteList
=========
 
This White Listing helper will html encode all tags and strip all attributes that aren't specifically allowed.  
It also strips href/src tags with invalid protocols, like javascript: especially.  It does its best to counter any
tricks that hackers may use, like throwing in unicode/ascii/hex values to get past the javascript: filters.  Check out
the extensive test suite.
 
  <%= white_list @article.body %>
 
You can add or remove tags/attributes if you want to customize it a bit.
 
Add table tags
  
  WhiteListHelper.tags.merge %w(table td th)
 
Remove tags
  
  WhiteListHelper.tags.delete 'div'
 
Change allowed attributes
 
  WhiteListHelper.attributes.merge %w(id class style)
 
white_list accepts a block for custom tag escaping.  Shown below is the default block that white_list uses if none is given.
The block is called for all bad tags, and every text node.  node is an instance of HTML::Node (either HTML::Tag or HTML::Text).  
bad is nil for text nodes inside good tags, or is the tag name of the bad tag.  
 
  <%= white_list(@article.body) { |node, bad| white_listed_bad_tags.include?(bad) ? nil : node.to_s.gsub(/</, '&lt;') } %>
  
Original plugin website: http://weblog.techno-weenie.net/2006/9/3/white-listing-plugin-for-rails
Original plugin SVN: http://svn.techno-weenie.net/projects/plugins/white_list/