(cmark >= 1.1.0)
CommonMark\CQL::__invoke — CQL Execution
   Shall invoke the current CQL function on the given root,
   executing the given handler on entry to a \CommonMark\Node
  
rootthe root node of a tree
handlershould have the prototype:
$root
      , \CommonMark\Node $entering
       ) : ?boolhandler fail to return (void), or return null, CQL will continue executing