Documentation on cms:LocalizedHyperlink

A customized widget built for us uses cms:LocalizedHyperlink to create a linked image on our site. However, the image's alt tag is empty, even though the image file it references has Description text in the image library. The custom widget does not have a field for alt text. Looking at the .ascx file, I see

<%@ Control Language="C#" AutoEventWireup="true" Inherits="CMSWebParts_[OurSite]_Global_WidgetBottomCalloutDetailPage" CodeFile="~/CMSWebParts/[OurSite]/Global/WidgetBottomCalloutDetailPage.ascx.cs" %>

<article class="widget02">
    <cms:LocalizedHyperlink ID="hlImage" runat="server"></cms:LocalizedHyperlink>
    <h3>
        <cms:LocalizedHyperlink ID="hlLink" runat="server"></cms:LocalizedHyperlink>
    </h3>
    <p>
        <asp:Literal runat="server" ID="ltrContent"></asp:Literal>
    </p>
</article>

The .cs file associated with this is:

using System;
using System.Data;
using System.Collections;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

using CMS.PortalControls;
using CMS.GlobalHelper;
using CMS.CMSHelper;

public partial class CMSWebParts_[OurSite]_Global_WidgetBottomCalloutDetailPage : CMSAbstractWebPart
{
    #region "Properties"

    public string Title
    {
        get
        {
            return ValidationHelper.GetString(GetValue("Title"), "");
        }
        set
        {
            SetValue("Title", value);
        }
    }

    public string Image
    {
        get
        {
            return ValidationHelper.GetString(GetValue("Image"), "");
        }
        set
        {
            SetValue("Image", value);
        }
    }

    public string Content
    {
        get
        {
            return ValidationHelper.GetString(GetValue("Content"), "");
        }
        set
        {
            SetValue("Content", value);
        }
    }

    public string Link
    {
        get
        {
            return ValidationHelper.GetString(GetValue("Link"), "");
        }
        set
        {
            SetValue("Link", value);
        }
    }

    public string LinkTarget
    {
        get
        {
            return ValidationHelper.GetString(GetValue("LinkTarget"), "");
        }
        set
        {
            SetValue("LinkTarget", value);
        }
    }

    #endregion


    #region "Methods"

    /// <summary>
    /// Content loaded event handler
    /// </summary>
    public override void OnContentLoaded()
    {
        base.OnContentLoaded();
        SetupControl();
    }


    /// <summary>
    /// Initializes the control properties
    /// </summary>
    protected void SetupControl()
    {
        if (this.StopProcessing)
        {
            // Do not process
        }
        else
        {
            hlImage.Visible = false;
            if (!String.IsNullOrEmpty(Image))
            {
                hlImage.Visible = true;
                hlImage.ImageUrl = Image;
                hlImage.NavigateUrl = Link;
            }

            hlLink.NavigateUrl = Link;
            hlLink.Text = Title;
            hlLink.Target = LinkTarget;

            ltrContent.Text = Content;
        }
    }


    /// <summary>
    /// Reloads the control data
    /// </summary>
    public override void ReloadData()
    {
        base.ReloadData();

        SetupControl();
    }

    #endregion
}

I've been searching for any documentation on cms:LocalizedHyperlink, but have not been able to find anything yet. I've been also looking in the various directories on our site for any file that looks like it might contain a LocalizedHyperlink function, but am also coming up empty. How can I pass the image Description into the hlImage's properties so that the LocalizedHyperlink code sticks it in the alt attribute?

-matt