In an Android ConstraintLayout, what is the tools:layout_constraintTop_creator attribute for?

In this code snippet, what does it mean to have the tools:layout_constraintTop_creator attribute set to "1"?

<TextView
    android:text="@string/passenger_label"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/textViewPassengerLabel"
    android:textAppearance="@style/TextAppearance.AppCompat.Caption"
    android:letterSpacing="0.5"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    android:layout_marginStart="16dp"
    android:layout_marginTop="16dp"
    android:layout_marginLeft="16dp"
    tools:layout_constraintTop_creator="1"
    tools:layout_constraintLeft_creator="1" />