Rules are used to dynamically alter the format of a data point, based on the value of the data point (or any other property of it).

Each rule has a condition expression; any plot parameter may be placed inside a rule to override the plot's default value for that parameter.

 <rules>
   <rule>
     condition    = var(value) > 0.6
     color        = red
     fill_color   = red
   </rule>
 </rules>