Automatic jQuery accordion from header tags

You can use shortcode function to do this.

function accordion_shortcode( $atts, $content = null ) {
   extract( shortcode_atts( array(
      'class' => 'accordion',
      ), $atts ) );

   return '<div class="' . esc_attr($class) . '">' . $content . '</div>';
}

add_shortcode( 'accordion', 'accordion_shortcode' );

In editor you wrap your content:

[accordion]
<h3>Headline 1</h3>
<p>Content.. lorem ipsum</p>

<h3>Headline 2</h3>
<p>Content.. lorem ipsum</p>

<h3>Headline 3</h3>
<p>Content.. lorem ipsum</p>
[/accordion]