file in the app module

<?xml version="1.0" encoding="utf-8"?>
<!--
  ~ Copyright (C) 2016 The Android Open Source Project
  ~
  ~ Licensed under the Apache License, Version 2.0 (the "License");
  ~ you may not use this file except in compliance with the License.
  ~ You may obtain a copy of the License at
  ~
  ~      http://www.apache.org/licenses/LICENSE-2.0
  ~
  ~ Unless required by applicable law or agreed to in writing, software
  ~ distributed under the License is distributed on an "AS IS" BASIS,
  ~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  ~ See the License for the specific language governing permissions and
  ~ limitations under the License.
  -->

<layout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto">
    <data>
        <variable name="name" type="String"/>
        <variable name="lastName" type="String"/>
        <variable name="anotherVariable" type="String"/>
    </data>
    <LinearLayout
            android:orientation="vertical" android:layout_width="match_parent"
            android:layout_height="match_parent">
        <include layout="@layout/included_in_app_layout" android:id="@+id/included"/>
    </LinearLayout>
</layout>

file in the library module

<!--
  ~ Copyright (C) 2016 The Android Open Source Project
  ~
  ~ Licensed under the Apache License, Version 2.0 (the "License");
  ~ you may not use this file except in compliance with the License.
  ~ You may obtain a copy of the License at
  ~
  ~      http://www.apache.org/licenses/LICENSE-2.0
  ~
  ~ Unless required by applicable law or agreed to in writing, software
  ~ distributed under the License is distributed on an "AS IS" BASIS,
  ~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  ~ See the License for the specific language governing permissions and
  ~ limitations under the License.
  -->

<layout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools">
    <data>
        <variable name="foo" type="String"/>
        <variable name="foo2" type="int"/>
    </data>
    <RelativeLayout android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:paddingLeft="@dimen/activity_horizontal_margin"
                    android:paddingRight="@dimen/activity_horizontal_margin"
                    android:paddingTop="@dimen/activity_vertical_margin"
                    android:paddingBottom="@dimen/activity_vertical_margin"
                    tools:context=".MainActivity">
        <TextView android:text='@{foo2 + " " + foo}' android:layout_width="wrap_content"
                  android:layout_height="wrap_content"/>

    </RelativeLayout>
</layout>

generated code

public class HasIncludeFromLibBinding extends android.databinding.ViewDataBinding  {

    private static final android.databinding.ViewDataBinding.IncludedLayouts sIncludes;
    private static final android.util.SparseIntArray sViewsWithIds;
    static {
        sIncludes = new android.databinding.ViewDataBinding.IncludedLayouts(2);
        sIncludes.setIncludes(0, 
            new String[] {"included_in_app_layout"},
            new int[] {1},
            new int[] {R.layout.included_in_app_layout});
        sViewsWithIds = null;
    }
    // views
    public final android.databinding.testlibrary.databinding.IncludedInAppLayoutBinding included;
    ....