@@ -868,10 +868,13 @@
 							idx = 1
 							fbimg = {
 								elt = 'img'; --fallback
 								attrs = {
-									alt = '';
+									alt = obj.props.desc or obj.props.detail or '';
+									title = obj.props.detail;
 									src = uri;
+									width = obj.props.width;
+									height = obj.props.height;
 								};
 							}
 						else idx = #ctr.nodes end
 						table.insert(ctr.nodes, idx, {
@@ -972,9 +975,30 @@
 					rtype[2](src, top)
 				end
 			end
 			local ft = flatten(top)
-			return ft
+			local cap = b.cap or obj.props.desc or obj.props.detail
+			if b.mode == 'inline' then
+				-- TODO insert caption
+				return ft
+			else
+				local prop = {}
+				if b.mode == 'open' then
+					prop.open = true
+				end
+				return tag('details', prop, catenate {
+					tag('summary', {},
+						 cap and (
+							 -- the block here should really be the relevant
+							 -- ref definition if an override caption isn't
+							 -- specified, but oh well
+							 sr.htmlSpan(spanparse(
+								 cap, b.origin
+							 ), b, s)
+						) or '');
+					ft;
+				})
+			end
 		end
 
 		function block_renderers.macro(b,s)
 			local all = renderSubdoc(b.doc)