Skins - simple question, really

If someone wouldn’t mind answering a simple question-

Say in prog.swf you have,

public var img_fg:SWFLoader;

and then later in prog.swf you call,

sbVert.setStyle("downArrowUpSkin",ScrollArrowSkinWR);

where ScrollArrowSkinWR is a ProgrammaticSkin class (defined in another file). What is the syntax to access img_fg from within ScrollArrowSkinWR.