Gtk+3 How to specify child properties of stack

I am new to gtk and I am trying to build a gtk application.

I went through the gtk tutorial to create gtk application.

I want to specify "gtk stack child property title" in xml which is loaded via gktbuilder.

How can I specify "gtk stack child property title" in xml and where can I get manual for the xml I cannot find it anywhere?

<?xml version="1.0" encoding="UTF-8"?>
<interface>
  <!-- interface-requires gtk+ 3.8 -->
  <object class="GtkWindow" id="window">
<property name="title" translatable="yes">GLocalshare</property>

<property name="default-width">600</property>
<property name="default-height">400</property>
<child>
  <object class="GtkBox" id="content_box">
    <property name="visible">True</property>
    <property name="orientation">vertical</property>
    <child>
      <object class="GtkHeaderBar" id="header">
        <property name="visible">True</property>
        <property name="show-close-button">True</property>

        <child type="title">
          <object class="GtkStackSwitcher" id="tabs">
            <property name="visible">True</property>
            <property name="margin">6</property>
            <property name="stack">stack</property>
    <child>
    </child>

      </object>
    </child>
          </object>
    </child>
    <child>
      <object class="GtkStack" id="stack">
        <property name="visible">True</property>
    <property name="visible-child">label1</property>
    <child>

      <object class="GtkLabel" id="label1">
    <property name="visible">True</property>
    <property name="label">label1</property>
    <property name="title">label1</property>
    <property name="name">label1</property>
      </object>
    </child>
    <child >

      <object class="GtkLabel" id="label2">
    <property name="title">label2</property>
    <property name="visible">True</property>
    <property name="label">label2</property>
    <property name="name">label2</property>
      </object>
       </child>
      </object>
    </child>
  </object>
</child>
 </object>
</interface>

You can find the documentation on this here, in the sections Child properties and GtkContainer as GtkBuildable:

The GtkContainer implementation of the GtkBuildable interface supports a <packing> element for children, which can contain multiple <property> elements that specify child properties for the child. An example of child properties in UI definitions:

<object class="GtkVBox">
  <child>
    <object class="GtkLabel"/>
    <packing>
      <property name="pack-type">start</property>
    </packing>
  </child>
</object>