title: attribute (android:textSize="?android:attr/textAppearanceMedium") throws error
body: <p>why does this attribute throw error "Binary XML file line #25: Error inflating class TextView"? my app crashed when i used the attribute to declare it to "?android:attr/textAppearanceMedium", but when i changed it to hard-coded "16sp" it worked without crashing. what is wrong with this attribute?    </p>
  
  <pre><code>&lt;i&gt;
  &lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:tools="http://schemas.android.com/tools"
      android:id="@+id/list_item"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:background="@color/tan_background"
      android:minHeight="@dimen/list_item_height"
      android:orientation="horizontal"&gt;
  
      &lt;ImageView
          android:id="@+id/image"
          android:layout_width="@dimen/list_item_height"
          android:layout_height="@dimen/list_item_height"
          android:background="@color/tan_background"
          android:src="@mipmap/ic_launcher" /&gt;
  
      &lt;LinearLayout
          android:id="@+id/textLayout"
          android:layout_width="match_parent"
          android:layout_height="@dimen/list_item_height"
          android:orientation="vertical"
          android:paddingLeft="16dp"&gt;
  
          &lt;TextView
              android:id="@+id/miwok_name"
              android:layout_width="match_parent"
              android:layout_height="0dp"
              android:textColor="@android:color/white"
              android:textSize="?android:attr/textAppearanceMedium"
              android:textStyle="bold"
              android:gravity="bottom"
              tools:text="lutti"
              android:layout_weight="1"/&gt;
  
          &lt;TextView
              android:id="@+id/default_name"
              android:layout_width="match_parent"
              android:layout_height="0dp"
              android:textColor="@android:color/white"
              android:textSize="?android:attr/textAppearanceMedium"
              tools:text="one"
              android:layout_weight="1"
              android:gravity="top"/&gt;
      &lt;/LinearLayout&gt;
  
  &lt;/LinearLayout&gt;
  &lt;/i&gt;
  </code></pre>