anchor.diff:  mode (`v`). The header name will match the supplied value (e.g.,
   `pid` versus `p`).  For example:
   
  -["source","sh",subs="attributes,callouts"]
  +[source,sh]
   --------------------------------------------------
   % curl 192.168.56.10:9200/_cat/nodes?v&h=id,ip,port,v,m
   id   ip            port v           m
  
positive.code: |Memory used by index writer |18mb
  |`segments.version_map_memory` |`svmm`, `segmentsVersionMapMemory` |No
  |Memory used by version map |1.0kb
  |=======================================================================
  
negative.code: merges |0b
  |`merges.total_time` |`mtt`, `mergesTotalTime` |No |Time spent merging
  documents |0s
  |`refresh.total` |`rto`, `refreshTotal` |No |Number of refreshes |16
  |`refresh.time` |`rti`, `refreshTime` |No |Time spent in refreshes |91ms
  |`script.compilations` |`scrcc`, `scriptCompilations` |No |Total script compilations |17
  