I am trying to understand how does <merge> tag internally work. I have studied some examples using View Hierarchy tool. So I understand basic using and how does it work on higher level, but I wanna to study more about this tag and inflating views in general.
So let's consider some simple layouts
activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://ift.tt/nIICcg"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/bg"
    android:gravity="center_horizontal">

<include layout="@layout/titlebar"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    />

<TextView android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:id="@+id/some_text"
    android:text="@string/hello"
    android:padding="10dp" />

</RelativeLayout>

And of course titlebar.xml

<merge xmlns:android="http://ift.tt/nIICcg"
    >

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/chrome" />
</merge>

In this case we have following result.

Let's change our titlebar.xml

<ImageView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@+id/some_text"
    android:src="@drawable/chrome" />

The result is really forthcoming.

Let's do more changes in our activity_main.xml file.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://ift.tt/nIICcg"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/bg"
    android:gravity="center_horizontal">

<include layout="@layout/titlebar"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    />

<TextView android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:id="@+id/bug"
    android:text="@string/hello"
    android:padding="10dp" />


    </LinearLayout>

And in titlebar.xml I left everything the same.

So in this case we have some weird things
1. Now our root layout is LinearLayout. We have specified nonexistent attribute android:layout_below="@+id/some_text" in titlebar file

2. In the same line we have another issue @+id/some_text doesn't exist anymore, now we have @+id/bug. Let's look at the result

Here I have some questions :

1. We are can use any attribute (for any layout) in merged file,but if the viewgroup(layout) where this part is included (in our case activity_main.xml) doesn't have such attributes, what how this situation is solved, just ignored as we can see in result ?

2. We have hardcoded id of view above imageview,it works if id is exists, but if it doesn't , as we can see in result it is also just being ignored

So I have already written a lot. To sum up, where works of XML parser exactly with merged and include tags is described, also it will be good to know where sources of XML parser is located, to look through it.

I will be grateful for everyone who read this line and can suggest something or give advice.

Thx in advance.