optimum

This attribute indicates the optimal numeric value. It must be within the range (as defined by the <code>min</code> attribute and <code>max</code> attribute). When used with the <code>low</code> attribute and <code>high</code> attribute, it gives an indication where along the range is considered preferable. For example, if it is between the <code>min</code> attribute and the <code>low</code> attribute, then the lower range is considered preferred.