示例10：value > high
进度：<meter value="0.9" high="0.8"></meter>
示例11：value < low
进度：<meter value="0.1" low="0.25"></meter> 
示例12：value = low
进度：<meter value="0.25" low="0.25"></meter> 
示例13：value > low
进度：<meter value="0.5" low="0.25"></meter>
示例14：optimum < low < value < high
进度：<meter low="0.25" optimum="0.15" high="0.75" value="0.5"></meter> 
示例15：low < optimum = value < high
进度：<meter low="0.25" optimum="0.5" high="0.75" value="0.5"></meter>
示例16：low < value < high < optimum
进度：<meter low="0.25" optimum="0.85" high="0.75" value="0.5"></meter> 
示例17：value < low < high < optimum
进度：<meter low="0.25" optimum="0.85" high="0.75" value="0.2"></meter> 
