How can I override a node's post date theme?

Question

HTML5 provides a time element, and a lot of modern sites are using the time element for their content post dates.

How can I override a node's post date theming, so I can change the rendering from a div element to a time element?

Currently, the markup looks like:

<div class="field__item even">2015-01-17</div>

I want it to render it as:

<time datetime="2015-01-17T12:00">2015-01-17</time>

I would like to handle this in my theme, since I have an Omega 4 subtheme I use as a base theme for client sites and want it to handle the functionality.

Answer 1

I'm using Display Suite, which takes over the node's created timestamp and turns it into a field named post_date. Therefore, I overrode the field.tpl.php file and named it field--post-date.tpl.php, and added the time element to the markup:

<div class="<?php print $classes; ?>"<?php print $attributes; ?>>
  <?php if (!$label_hidden): ?>
    <div class="field-label"<?php print $title_attributes; ?>><?php print $label ?>:&nbsp;</div>
  <?php endif; ?>
  <div class="field-items"<?php print $content_attributes; ?>>
    <?php foreach ($items as $delta => $item): ?>
      <div class="field-item <?php print $delta % 2 ? 'odd' : 'even'; ?>"<?php print $item_attributes[$delta]; ?>><time datetime="<?php print $datetime; ?>"><?php print render($item); ?></time></div>
    <?php endforeach; ?>
  </div>
</div>

To get the $datetime variable, I added the following code to theme_preprocess_field():

function mytheme_preprocess_field(&$vars) {
    // check for Display Suite fields.
    if ($vars['element']['#field_type'] != 'ds') {
        return;
    }
    switch ($vars['element']['#field_name']) {
        case 'post_date':
            if ($vars['element']['#entity_type'] != 'node') {
                break;
            }
            $node = $vars['element']['#object'];
            $vars['datetime'] = date_iso8601($node->created);
        break;
    }
}

I'm just handling nodes, and a node always has one created time. The loop in the tpl file can probably be removed, since there will always be one value.