/** @throws SyntaxException if the given string is not a vaild ActionScript 3 expression. */
 public Expression newExpression(String expr) {
   LinkedListTree ast = AS3FragmentParser.parseExpr(expr);
   // ANTLR creates a 'nil' parent node (in case the result is a
   // list).  We break the link to that parent because we assert
   // the parent is null when child nodes are attached elsewhere
   // in the tree.
   ast.setParent(null);
   return ExpressionBuilder.build(ast);
 }
 public Expression dup(Expression expr) {
   LinkedListTree ast = ASTUtils.ast(expr);
   return ExpressionBuilder.build(ASTBuilder.dup(ast));
 }