Adding an icon before a chapter title

Hi everybody,

I would like to dynamically add an icon before a chapter title, with a possibility to change the icon file's name in the XML file itself, and not in the stylesheet. I would like to add the icon's filename in the chapter's tag itself (e.g. <chapter icon="internetconn"> and to pass this filename to the template that will add it to the rest of the file path (eg, concatenate('/images', @icon, '.png')

Please advise, how to extract the value of the "icon" variable and pass it to the "concatenate" part of the <fo-external graphic> template?

Thanks a lot!
Nancy