anchor.diff:  * `!`: Not
   * Range operator `(-)` : a value such as `"3-5"` means a value between 3 to 5 (inclusive). This is only supported in the following attributes
   ** `replica`
  +** array operator . e.g: `sysprop.zone = ["east", "west","apac"]`. This is equivalent to having multiple rules with each of these values. This can be used in the following attributes
  +** `sysprop.*`
  +** `port`
  +** `ip_*`
  +** `node`
  +** `diskType`
   * None means equal
   
   ==== Special functions
  
positive.code: ** `replica`
  ** `freedisk`
  * `#ALL` : This is applied to the `replica` attribute only. This means all replicas qualifying a certain clause
  * `#EQUAL`:  This is applied to the `replica` attribute only. This means equal no:of replicas in each bucket
  
  === Examples of Policy Rules
  
  
negative.code: [source,json]
  {"replica": "#ALL", "freedisk": ">500"}
  
  Keep all replicas in nodes with over `50%` freedisk
  [source,json]
  {"replica": "#ALL", "freedisk": ">50%"}
  
  