code: function _isBlankNode(v) {
    // Note: A value is a blank node if all of these hold true:
    // 1. It is an Object.
    // 2. If it has an @id key its value begins with '_:'.
    // 3. It has no keys OR is not a @value, @set, or @list.
    var rval = false;
    if(_isObject(v)) {
      if('@id' in v) {
        rval = (v['@id'].indexOf('_:') === 0);
      }
      else {
        rval = (Object.keys(v).length === 0 ||
          !(('@value' in v) || ('@set' in v) || ('@list' in v)));
      }
    }
    return rval;
  }
docs: Returns true if the given value is a blank node.
  
  @param v the value to check.
  
  @return true if the value is a blank node, false if not.