OutliningTagger_ReparseFile.cs

void ReparseFile(object sender, EventArgs args)
{
    ITextSnapshot snapshot = _buffer.CurrentSnapshot;

    List<MarkdownSection> newSections = new List<MarkdownSection>(
        MarkdownParser.ParseMarkdownSections(snapshot)
                      .Select(t => new MarkdownSection()
                      {
                          TokenType = t.TokenType,
                          Span = snapshot.CreateTrackingSpan(t.Span, SpanTrackingMode.EdgeExclusive)
                      }));

    var oldSectionSpans = new NormalizedSnapshotSpanCollection(
        _sections.Select(s => s.Span.GetSpan(snapshot)));
    var newSectionSpans = new NormalizedSnapshotSpanCollection(
        newSections.Select(s => s.Span.GetSpan(snapshot)));

    var first = NormalizedSnapshotSpanCollection.Difference(oldSectionSpans, newSectionSpans);
    var second = NormalizedSnapshotSpanCollection.Difference(newSectionSpans, oldSectionSpans);

    var difference = NormalizedSnapshotSpanCollection.Union(first, second);

    _sections = newSections;

    foreach (var span in difference)
    {
        var temp = TagsChanged;
        if (temp != null)
            temp(this, new SnapshotSpanEventArgs(span));
    }
}