title: ConstraintLayout: What does `layout_constraintLeft_creator` do in xml?
body: <p>Example code:</p>
  
  <pre><code> &lt;EditText
          android:id="@+id/msg_type"
          android:layout_width="0dp"
          android:layout_height="40dp"
          android:layout_marginBottom="8dp"
          android:layout_marginEnd="8dp"
          android:layout_marginStart="8dp"
          android:hint="Input message"
          app:layout_constraintBottom_toBottomOf="parent"
          app:layout_constraintHorizontal_bias="0.75"
          app:layout_constraintLeft_toLeftOf="parent"
          app:layout_constraintRight_toLeftOf="@+id/btn_chat_send"
          tools:layout_constraintBottom_creator="1"
          tools:layout_constraintLeft_creator="1"
          tools:layout_constraintRight_creator="1"/&gt;
  </code></pre>
  
  <p>What does <code>tools:layout_constraintRight_creator="1"</code> do here? There aren't any document explaining these things.</p>