After using the Unobtrusive Code Highlighter for sometime I decided to extend it to support nested rules. For example, if a keyword is in a string that keyword should still be highlighted appropriately. I currently use this library for C#, XAML, Ruby, Javascript, CSS, HTML, and Radius coding examples. The new implementation takes the concepts of HighlightStyle and HightlightRule and implements them as prototype classes; the beta is included in the download package you can get here Below are a sample from each language:

C#


  public abstract class MyClassName
  {
     private List<string> _myMemberVariable = new List<string>();
     public List<string> MyMemberVariable
     {
       get { return _myMemberVariable; }
       set { _myMemberVariable = value; }
     }

    // Remark: Comments are colored correctly
    public void MyMethod(int myParam)
    {
      Console.Out.PrintLine("C# Code Formatting!");
    }
  }

XAML 


   <!-- Here are some XAML comments -->
   <Color x:Key="MyBackColor" R="#80" G="#80" B="#C8" A="#FF" />  
   <Style x:Key="ActiveRectangle" TargetType="{x:Type Rectangle}" >  
     <Style.Triggers>  
       <Trigger Property="IsMouseOver" Value="True">  
         <Setter Property="Fill" Value="{ce:RelativeColor BaseColorKey=MyBackColor,Style=Lighten}"/>  
       </Trigger>  
       <Trigger Property="IsMouseOver" Value="False">  
         <Setter Property="Fill" Value="{ce:RelativeColor BaseColorKey=MyBackColor,Style=Normal}"/>  
      </Trigger>  
    </Style.Triggers>  
  </Style>

Ruby


  def to_xml(options = {})
    options[:indent] ||= 2
    xml = options[:builder] ||= Builder::XmlMarkup.new(:indent => options[:indent])
    xml.instruct! unless options[:skip_instruct]
    xml.tag!("form-response", :id => id) do
      xml.tag!("created-at", created_at.strftime("%Y-%m-%d %H:%M")) if options[:show_timestamps]
      content.each do |name, value|
        if(!options[:fields].nil? && options[:fields].include?(name))
          xml.tag!(name.dasherize, value)
        end
      end
    end
  end

HTML


  <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
  <html xmlns="http://www.w3.org/1999/xhtml">
  <head>
    <link href="/styles.css" media="all" rel="stylesheet" type="text/css" />
  </head>
  <body>
    <div id="container">
      <h1>Sample HTML Content</h1>
    </div>
  </body>
  </html>

Radius


  <r:children:each by="published_at" order="desc" limit="10">
    <r:snippet name="article" />
  </r:children:each>

CSS


  /*--------------------------------------------------------------
   C#
  --------------------------------------------------------------*/
  #content pre code.sharp { color: white; }
  #content code.csharp span.comment   { color: #66cc33;  }
  #content code.csharp span.string    { color: #a31515;  }
  #content code.csharp span.keywords  { color: #3387cc;  }

Javascript


  HighlightStyle.prototype.parse = function(text, ignoreCase) {
    // main text parsing and replacement
    var rules = this.styleRules;

    return text.replace(new RegExp(this.styleRules, (ignoreCase) ? "gi" : "g"), function() {
        var i = 0, j = 1, rule;
        while (rule = rules[i++]) {
            if (arguments[j]) {
                // if no custom replacement defined do the simple replacement
                if (rule.replacement == null) {
                    return "" + arguments[0] + "";
                } else {
                    // replace $0 with the className then do normal replaces
                    var str = rule.replacement.replace("$0", rule.className);
                    for (var k = 1; k <= rule.length - 1; k++) str = str.replace("$" + k, arguments[j + k + 1]);
                    return str;
                }
            } else j += rule.length;
        }
    });
  }