PARIS — The joy is back in fashion. And that was certainly clear in the spring collection Marc Jacobs showed for Louis Vuitton. There was vim, vigor and vitality — not to mention plenty of charm — in such looks as his lace dresses trimmed with black ribbon, flowered pastel frocks and narrow striped knits. Here, one of Jacobs’ intriguing proportion plays: a bilevel tiered jacket over a short full skirt. For more on Paris, see pages 4 to 8.