Render Control into HTML String

Occasionally there is a need to get string representation of ASP.NET control in other words - render it into string instead of letting it be rendered on the page. The following method renders a control into its HTML string.
Namespaces used:

using System.Text;
using System.IO;
using System.Web.UI;

public string RenderControl(Control ctrl) 
{
    StringBuilder sb = new StringBuilder();
    StringWriter tw = new StringWriter(sb);
    HtmlTextWriter hw = new HtmlTextWriter(tw);

    ctrl.RenderControl(hw);
    return sb.ToString();
}