C#

protected override void OnMouseMove(MouseEventArgs e)
{
    base.OnMouseMove(e);

    bool foundItem = false;
    int index = -1;

    foreach (TabPage page in this.TabPages)
    {
        index++;
        if (this.GetTabRect(index).Contains
            (e.Location) == true)
        {
            _hoverIndex = index;
            this.Invalidate();
            foundItem = true;

            if (this.TabMouseEnter != null)
            {
                TabMouseEventArgs tabArgs = new TabMouseEventArgs();
                tabArgs.TabPage = page;

                this.TabMouseEnter(this, tabArgs);
            }
        }
        else if (foundItem == false)
        {
            _hoverIndex = -1;
            this.Invalidate();

            if (this.TabMouseLeave != null)
            {
                TabMouseEventArgs tabArgs = new TabMouseEventArgs();
                tabArgs.TabPage = page;

                this.TabMouseLeave(this, tabArgs);
            }
        }
    }

    if (e.Button == MouseButtons.Left)
    {
        if (_hoverIndex != -1)
        {
            // Store the current DockStyle to a variable so we can re-use it when we
            // will re-add all the remaining Forms to the parent DockPane.

            DockStyle dockStyle = this.DockPanel.Dock;

            // Aaaand hide the dock Rectangles.

            this.DockPanel.DockPane.HideDockRectangles();

            // We should now create a new DockForm with the dragging TabPage's contents.

            DockForm dockForm = new DockForm();
            DockPanel dockPanel = this.DockPanel;

            this.DockPanel.DockPane.Controls.Remove(dockPanel);
            dockPanel.Dock = DockStyle.Fill;

            dockForm.Location = Cursor.Position;
            dockForm.Controls.Add(dockPanel);
            dockForm.Renderer = this.Renderer;
            dockForm.Show();

            this.DockPanel.DockForm = dockForm;

            // Loop through all the TabPages of the DockTab and remove all TabPages that
            // are not the MainTabPage of the parent DockPanel.

            List<TabPage> removePages = new List<TabPage>();
            foreach (TabPage page in this.TabPages)
            {
                if (page != this.DockPanel.MainTabPage)
                    removePages.Add(page);
            }

            // We found all the tabs that needs to be removed - remove them from this
            // DockTab, and re-add their contents to the DockPane.

            foreach (TabPage page in removePages)
            {
                foreach (Control control in page.Controls)
                {
                    if (control is DockContainer)
                    {
                        DockContainer container = control as DockContainer;
                        this.DockPanel.DockPane.CreatePanel(container.Form, dockStyle); // Add the found Form to the parent DockPane.

                        // Finally remove the TabPage.
                        this.TabPages.Remove(page);
                    }
                }
            }
        }
    }
}