Function to render Bootstrap 3 Accordion markup from a ProcessWire PageArray

bs3AccordionMarkup.php

/*render a Bootstrap 3 accordion from a PW PageArray
variables passed to this function
$pages: PageArray the children of which will be rendered into an accordion
$title: string, name of the field to be used as panel title, eg "title"
$content: string, name of the field to be used as panel content, eg "bodycopy"
$accordion = "<div class='panel-group' id='accordion' role='tablist' aria-multiselectable='true'>";
*/
function bs3AccordionMarkup($pages, $titlefield, $contentfield) {

    $accordion = "<div class='panel-group' id='accordion' role='tablist' aria-multiselectable='true'>";

    $i = 1;
    foreach ($pages as $child) {
        $in = ($i == 1) ? " in" : "";
        $collapsed = ($i != 1) ? " class='collapsed'" : "";
        $accordion .= "  <div class='panel panel-default'>
        <div class='panel-heading' role='tab' id='heading$i'>
          <h3 class='panel-title'>
            <a$collapsed data-toggle='collapse' data-parent='#accordion' href='#collapse$i' aria-expanded='true' aria-controls='collapse$i'>
              {$child->$titlefield}
            </a>
          </h3>
        </div>
        <div id='collapse$i' class='panel-collapse collapse$in' role='tabpanel' aria-labelledby='heading$i'>
          <div class='panel-body'>
          {$child->$contentfield}
          </div>
        </div>
      </div>";
      $i++;
    }

    $accordion .= "</div>";
    return $accordion;
}