[Export(typeof(ITaggerProvider))]
    [TagType(typeof(SquiggleTag))] // this will probably be "IErrorTag" in the next release
    [ContentType("text")]          // "text" is the base of basically all content types

    internal sealed class ToDoTagger : ITagger<SquiggleTag>
    {
        // Our simple tagger can ignore this for now

    [Export(typeof(ITaggerProvider))]
    [TagType(typeof(SquiggleTag))] // this will probably be "IErrorTag" in the next release
    [ContentType("text")]          // "text" is the base of basically all content types

// starting with a SnapshotPoint, text line, or SnapshotSpan
SnapshotPoint point;
ITextSnapshotLine line = point.GetContainingLine();

// Make the background goldenrod yellow :)
 
    [Export(typeof(IWpfTextViewCreationListener))]

using System.ComponentModel.Composition;
using Microsoft.VisualStudio.Utilities;
using Microsoft.VisualStudio.Text.Editor;

//// Moving to a new visual line
 
// Assuming you have ITextView textView

//// Using the caret directly
 
// assuming you have ITextView textView

using System;
using System.Collections.Generic;
using System.ComponentModel.Composition;

testing gist