anchor.diff:  output its available columns. For example:
   
   [source,console]
  ---------------------------------------------------
  -GET /_cat/master?help
  ---------------------------------------------------
  +----
  +GET _cat/master?help
  +----
   
   Might respond with:
   
   [source,txt]
  ---------------------------------------------------
  +----
   id   |   | node id
   host | h | host name
   ip   |   | ip address
   node | n | node name
  ---------------------------------------------------
  +----
   // TESTRESPONSE[s/[|]/[|]/ non_json]
   
   NOTE: `help` is not supported if any optional url parameter is used.
  
positive.code: only those columns to appear. For example:
  
  [source,console]
  --------------------------------------------------
  GET /_cat/nodes?h=ip,port,heapPercent,name
  --------------------------------------------------
  
  Responds with:
  
  [source,txt]
  --------------------------------------------------
  127.0.0.1 9300 27 sLBaIGK
  --------------------------------------------------
  // TESTRESPONSE[s/9300 27 sLBaIGK/\\d+ \\d+ .+/ non_json]
  
  You can also request multiple columns using simple wildcards like
  
negative.code: sorted in ascending order by column1, in descending order by column2, and in ascending
  order by column3.
  
  [source,console]
  ----
  GET _cat/templates?v=true&s=order:desc,index_patterns
  ----
  
  returns:
  
  [source,txt]
  ----
  name                  index_patterns order version
  pizza_pepperoni       [*pepperoni*]  2
  sushi_california_roll [*avocado*]    1     1
  pizza_hawaiian        [*pineapples*] 1
  ----
  
  include::cat/alias.asciidoc[]
  
  