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> |
示例18：optimum < low < high < value
| 进度：<meter low="0.25" optimum="0.2" high="0.75" value="0.8"></meter> |
