code: private Long markCoveredTokens(Map<SNode, Long> markedAndCovered, SNode tok) {
  		RelannisNodeFeature f = RelannisNodeFeature.extract(tok);
  		if (markedAndCovered.containsKey(tok) && f != null && f.getMatchedNode() == null) {
  			return markedAndCovered.get(tok);
  		}
  		return f != null ? f.getMatchedNode() : null;
  	}
docs: Checks if a token is covered by a matched node but not a match by it self.
  
  @param markedAndCovered A mapping from node to a matched number. The node
  must not matched directly, but covered by a matched
  node.
  @param tok              the checked token.
  @return Returns null, if token is not covered neither marked.