code: private GrammaticalStructure tagDependencies(Tree tree, boolean makeCopulaVerbHead) {
          SemanticHeadFinder headFinder = new SemanticHeadFinder(!makeCopulaVerbHead); // keep copula verbs as head
          // string -> true return all tokens including punctuations.
          GrammaticalStructure gs = new EnglishGrammaticalStructure(tree, string -> true, headFinder);
          return gs;
      }
docs: What is Mary happy about? -- copula