title: Difference between android:width and android:layout_width
body: <p>in the following code why the appearance of the <em>radio button</em> changes when i set </p>
  
  <pre><code> android:layout_width="fill_parent"
  </code></pre>
  
  <p>and</p>
  
  <pre><code> android:width="fill_parent"
  </code></pre>
  
  <p>i am talking about the _radio button _ whose id is <code>left</code></p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent"
  android:orientation="vertical" &gt;
  
  &lt;RadioGroup
      android:id="@+id/orientation"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:orientation="horizontal"
      android:padding="5px" &gt;
  
      &lt;RadioButton
          android:id="@+id/horizontal"
          android:text="horizontal" /&gt;
  
      &lt;RadioButton
          android:id="@+id/vertical"
          android:text="vertical" /&gt;
  &lt;/RadioGroup&gt;
  
  &lt;RadioGroup
      android:id="@+id/gravity"
      android:layout_width="fill_parent"
      android:layout_height="wrap_content"
      android:orientation="vertical"
      android:padding="5px"
  
       &gt;
  
      &lt;RadioButton
          android:id="@+id/left"
          android:text="left"
          android:layout_width="fill_parent"   // I am talking about this line
          /&gt;
  
      &lt;RadioButton
          android:id="@+id/center"
          android:text="center" /&gt;
  
      &lt;RadioButton
          android:id="@+id/right"
          android:text="right" /&gt;
  &lt;/RadioGroup&gt;
  </code></pre>
  
  <p></p>