This class implements a keyword map. It implements a digital search trees (tries) to find a word.
		public HighlightRuleSet(XmlElement el)
		{
			XmlNodeList nodes;
			
			if (el.Attributes["name"] != null) {
				Name = el.Attributes["name"].InnerText;
			}
			
			if (el.HasAttribute("escapecharacter")) {
				escapeCharacter = el.GetAttribute("escapecharacter")[0];
			}
			
			if (el.Attributes["reference"] != null) {
				reference = el.Attributes["reference"].InnerText;
			}
			
			if (el.Attributes["ignorecase"] != null) {
				ignoreCase  = Boolean.Parse(el.Attributes["ignorecase"].InnerText);
			}
			
			for (int i  = 0; i < Delimiters.Length; ++i) {
				delimiters[i] = false;
			}
			
			if (el["Delimiters"] != null) {
				string delimiterString = el["Delimiters"].InnerText;
				foreach (char ch in delimiterString) {
					delimiters[(int)ch] = true;
				}
			}
			
//			Spans       = new LookupTable(!IgnoreCase);

			keyWords    = new LookupTable(!IgnoreCase);
			prevMarkers = new LookupTable(!IgnoreCase);
			nextMarkers = new LookupTable(!IgnoreCase);
			
			nodes = el.GetElementsByTagName("KeyWords");
			foreach (XmlElement el2 in nodes) {
				HighlightColor color = new HighlightColor(el2);
				
				XmlNodeList keys = el2.GetElementsByTagName("Key");
				foreach (XmlElement node in keys) {
					keyWords[node.Attributes["word"].InnerText] = color;
				}
			}
			
			nodes = el.GetElementsByTagName("Span");
			foreach (XmlElement el2 in nodes) {
				Spans.Add(new Span(el2));
				/*
				Span span = new Span(el2);
				Spans[span.Begin] = span;*/
			}
			
			nodes = el.GetElementsByTagName("MarkPrevious");
			foreach (XmlElement el2 in nodes) {
				PrevMarker prev = new PrevMarker(el2);
				prevMarkers[prev.What] = prev;
			}
			
			nodes = el.GetElementsByTagName("MarkFollowing");
			foreach (XmlElement el2 in nodes) {
				NextMarker next = new NextMarker(el2);
				nextMarkers[next.What] = next;
			}
		}
		public HighlightRuleSet()
		{
			keyWords    = new LookupTable(false);
			prevMarkers = new LookupTable(false);
			nextMarkers = new LookupTable(false);
		}