The RadSyntaxEditor control works with the underlying document with the help of taggers. Taggers are used to identify spans of text and assign them a specific tag if they match a specific condition. The matched tags are then processed by the UI layers which color the text or draw additional elements on screen.

Predefined Taggers

The RadSyntaxEditor comes with a number of predefined taggers:

  • CSharpTagger: A tagger responsible for the syntax-highlighting in the C# programming language.
  • VisualBasicTagger: A tagger responsible for the syntax-highlighting in the Visual Basic programming language.
  • JavaScriptTagger: A tagger responsible for the syntax-highlighting in the JavaScript programming language.
  • XmlTagger: A tagger responsible for the syntax-highlighting in the XML programming language.
  • SqlTagger: A tagger responsible for the syntax-highlighting in the T-SQL (Transact-SQL) programming language.
  • FoldingTagger: A tagger responsible for creating folding regions in code.
  • TextSearchHighlightTagger: A tagger which prepares collection of TextHighlightTag for all occurrences of a given search word.
  • TextSearchUnderlineTagger: A tagger which prepares collection of UnderlineTag for all occurrences of a given search word.

Register a Tagger

To be able to use these taggers in the RadSyntaxEditor control, you first need to register them in its TaggersRegistry.

Example 1: Registering taggers

var cSharpTagger = new CSharpTagger(this.syntaxEditor); 
var textSearchTagger = new TextSearchHighlightTagger(this.syntaxEditor, TextSearchHighlightTagger.SearchFormatDefinition); 

Custom Tagger

To create a custom tagger, you can inherit from the abstract generic TaggerBase class. You then need to implement the abstract GetTags class which is responsible for acquiring all spans of tags which meet a specific condition.

To demonstrate this we will create the following class which shows a tooltip on all occurrences of a specified search word.

Example 2: Registering taggers

public class SimpleToolTipTagger : TaggerBase<ToolTipTag> 
    private string searchWord; 
    public SimpleToolTipTagger(ITextDocumentEditor editor) 
        : base(editor) 
    public override IEnumerable<TagSpan<ToolTipTag>> GetTags(NormalizedSnapshotSpanCollection spans) 
        if (string.IsNullOrEmpty(this.searchWord)) 
            yield break; 
        TextSnapshot snapshot = this.Document.CurrentSnapshot; 
        foreach (TextSnapshotSpan snapshotSpan in spans) 
            string lineString = snapshotSpan.GetText(); 
            int index = lineString.IndexOf(this.searchWord); 
            while (index != -1) 
                TextSnapshotSpan tempSnapshotSpan = new TextSnapshotSpan(snapshot, 
                    new Span(snapshotSpan.Start + index, searchWord.Length)); 
                yield return new TagSpan<ToolTipTag>(tempSnapshotSpan, new ToolTipTag("Sample tooltip " + searchWord)); 
                index = lineString.IndexOf(this.searchWord, index + this.searchWord.Length); 
    public void UpdateSearchWord(string newSearchWord) 
        this.searchWord = newSearchWord; 
To use the tagger you need to register it in the TaggersRegistry as you would do with any other tagger. You can then call the UpdateSearchWord method to apply the tagger to any spans containing a specific word.

Example 3: Using the custom tagger

var simpleToolTipTagger = new SimpleToolTipTagger(this.syntaxEditor); 

Figure 1: The custom tooltip tagger

The custom tooltip tagger

See Also

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