RSS Responsive Caption

The problem:

Readers who use Google Reader to read WordPress powered website RSS feeds on their small-screen mobile devices don’t get the full picture if the WordPress site in question uses the caption short code functionality, because the resulting inline CSS code that displays does not instruct the feed reader to scale the image down to fit the screen.

See, i.e.:

In this image, a giant photo in a post is poorly displayed in Google Reader as a result of the default settings of WordPress 3.3 (and previous versions that include the Caption feature). As displayed on my Android-powered Nexus S from Google, running the latest version of Google Reader, Version 1.1.1.

The solution:

I created a new WordPress plugin called RSS Responsive Caption to adjust the inline CSS styles that get attached to images with captions to make them more “responsive.”

Really, all that was needed was the following CSS code to specify that the maximum width of an image should be 100% (of the screen size). That’s responsive web design, in a nutshell.

max-width: 100% !important;
height: auto;

Creating a plugin to accomplish this was not necessary. In fact, anyone can do this without downloading the plugin, simply (heh) by altering lines 745-746 in the wp-includes/media.php file, from:

return ‘<div ‘ . $id . ‘class=”wp-caption ‘ . esc_attr($align) . ‘” style=”width: ‘ . (10 + (int) $width) . ‘px”>’
. do_shortcode( $content ) . ‘<p>’ . $caption . ‘</p></div>’;


return ‘<div ‘ . $id . ‘class=”wp-caption ‘ . esc_attr($align) . ‘” style=”max-width: 100% !important; height: auto; width: ‘ . (10 + (int) $width) . ‘px”>’
. do_shortcode( $content ) . ‘<p>’ . $caption . ‘</p></div>’;

But! If I did it that way, then every time WordPress would release a new version of its frickin-awesome open source software package, I would have to manually go into the media.php file and change that line of code to keep my RSS feeds displaying properly in Google Reader.

Instead, I prefer the instant update method of installing the latest version of WordPress. I click the button, it does its thing and in a few moments of anticipatory suspense, I have the latest version of WordPress in all its glory, and I can troubleshoot it because my own specific modifications are separate.

That’s also why I typically choose to create child themes on top of existing themes – if the theme is ever updated by the theme author, I won’t have to manually sort out what was changed vs. how I reconfigured it, unless the theme author specifically chose to alter something I wanted to alter.

The plugin makes the viewing experience in Google Reader much better.

See, i.e.:

The photo as displayed in the RSS feed when the plugin is activated.

Download my first-ever WordPress plugin here:

RSS Responsive Caption


This plugin would not have been possible if the WordPress core team didn’t create a way to “allow a plugin to replace the content that would otherwise be returned” via the caption shortcode function (see: wp-includes/media.php, line 711), or, if they didn’t further explain the add_filter function in the codex, even going so far as suggesting the following plugin:

add_filter('img_caption_shortcode', 'my_img_caption_shortcode_filter',10,3);

 * Filter to replace the  shortcode text with HTML5 compliant code
 * @return text HTML content describing embedded figure
function my_img_caption_shortcode_filter($val, $attr, $content = null)
		'id'	=> '',
		'align'	=> '',
		'width'	=> '',
		'caption' => ''
	), $attr));

	if ( 1 > (int) $width || empty($caption) )
		return $val;

	$capid = '';
	if ( $id ) {
		$id = esc_attr($id);
		$capid = 'id="figcaption_'. $id . '" ';
		$id = 'id="' . $id . '" aria-labelledby="figcaption_' . $id . '" ';

	return '<figure ' . $id . 'class="wp-caption ' . esc_attr($align) . '" style="width: '
	. (10 + (int) $width) . 'px">' . do_shortcode( $content ) . '<figcaption ' . $capid
	. 'class="wp-caption-text">' . $caption . '</figcaption></figure>';

Basically, I took the plugin above and altered it to fit my needs, after an exhaustive search to determine that someone else hadn’t already done what I wanted to do.

I got the idea for this plugin by looking at the HTML source code of the posts WordPress generates for images with captions and images without, then Googling until I discovered what made what worked.

Articles and forum posts that I came across in the exploratory process include, but are likely not limited to:

Want to further alter the way captions are handled in WordPress? This plugin looks very interesting:

About RSS Responsive Caption
from the documentation section of the plugin:

This plugin allows publishers to better control the width of photos that use the WordPress caption shortcode feature, when that content is displayed in RSS feed readers like Google Reader, as displayed on small-screen mobile devices.

This plugin accomplishes the same thing that adjusting the “function img_caption_shortcode” code in includes/media.php would, but allows the user to automatically update WordPress without worrying about losing these changes.

It is the author’s hope that in future releases of WordPress (post 3.3), this plugin will prove unnecessary if (hard-working, responsive-minded) WordPress core developers decide to include the fix in newer versions of the awesome great open source software we have all come to love.

(Hint, hint)

Download my first-ever WordPress plugin here:

RSS Responsive Caption



3 thoughts on “RSS Responsive Caption”

    1. Enterpr1se, to answer your question, yes. Yes my plugin is still necessary; I just tested it on my own blog. Deactivating the plugin and posting a new post … then viewing the post in Google Reader proves that the images are still not being constrained to the reader’s window size, making for an awkward side-scrolling problem. Going to reactivate my plugin now!

  1. thanks for sorting this out for the rest of us. good thinking. a modest contribution yet a clever and useful one.

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