title: How to add a custom button state
body: <p>For instance, the default button has the following dependencies between its states and background images:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;selector xmlns:android="http://schemas.android.com/apk/res/android"&gt;
      &lt;item android:state_window_focused="false" android:state_enabled="true"
          android:drawable="@drawable/btn_default_normal" /&gt;
      &lt;item android:state_window_focused="false" android:state_enabled="false"
          android:drawable="@drawable/btn_default_normal_disable" /&gt;
      &lt;item android:state_pressed="true" 
          android:drawable="@drawable/btn_default_pressed" /&gt;
      &lt;item android:state_focused="true" android:state_enabled="true"
          android:drawable="@drawable/btn_default_selected" /&gt;
      &lt;item android:state_enabled="true"
          android:drawable="@drawable/btn_default_normal" /&gt;
      &lt;item android:state_focused="true"
          android:drawable="@drawable/btn_default_normal_disable_focused" /&gt;
      &lt;item
          android:drawable="@drawable/btn_default_normal_disable" /&gt;
  &lt;/selector&gt;
  </code></pre>
  
  <p>How can I define my own custom state (smth like <code>android:state_custom</code>), so then I could use it to dynamically change my button visual appearance?</p>