title: Layout-start-end,left-right concepts
body: <p>I am little confused regarding usage of below attributes.</p>
  
  <pre><code>&gt; android:layout_marginRight and   android:layout_marginEnd
  &gt; android:layout_marginLeft and android:layout_marginStart
  &gt; android:layout_toLeftOf and android:layout_toStartOf
  &gt; android:layout_toRightOf and android:layout_toEndOf
  &gt; android:layout_gravity="right|end"
  &gt; android:layout_gravity="left|start"
  </code></pre>
  
  <p>Below are the some of facts which i have mentioned.Please correct me if i am wrong.</p>
  
  <ul>
  <li><p>To support both Ltr and Rtl layouts  and to support versions prior to api level 17
  is it advisable to put the above attributes always in pairs..</p></li>
  <li><p>The "start" and "end" concepts were added in API Level 17 and will<br>
  take precedence for Ltr device with api level>=17  and "right" and "left"
  concepts will take precedence for Ltr device with api level&lt;17</p></li>
  <li><p>If our app minskdversion is >=17 then we can ignore "right" and<br>
  "left" attributes and use "start" and "end" attributes only</p></li>
  <li>The "start" and "end" concepts will take precedence in all Rtl
  devices</li>
  </ul>
  
  <p>Also I would like to know if there is any adverse effect in terms of performance/optimization if i add above attributes in pairs like-</p>
  
  <pre><code> &lt;TextView
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"
       android:layout_gravity="right|end"
       android:layout_marginRight="@dimen/dp10"
       android:layout_marginEnd="@dimen/dp10"
       android:layout_marginLeft="@dimen/dp10"
       android:layout_marginStart="@dimen/dp10"
       android:layout_toLeftOf="@+id/bar"
       android:layout_toStartOf="@+id/bar"
       /&gt;
  </code></pre>