Bootstrap内联子标题

<h1>I'm heading1 h1. <small>I'm secondary heading1 h1</small></h1> 
<h2>I'm heading2 h2. <small>I'm secondary heading2 h2</small></h2>
<h3>I'm heading3 h3. <small>I'm secondary heading3 h3</small></h3>
<h4>I'm heading4 h4. <small>I'm secondary heading4 h4</small></h4>
<h5>I'm heading5 h5. <small>I'm secondary heading5 h5</small></h5>
<h6>I'm heading6 h6. <small>I'm secondary heading1 h6</small></h6>