So how do you align a picture caption under a picture tag to it's right hands edge?

Attempted using div but clearly that isn't permitted in wordpress.

What alternative css/tags should i use?

Performs this not work?

.wordpress-caption p.wordpress-caption-text

I emerged with a method to specify alignment on the per-caption basis.

Essentially, I replicated the caption shortcode in the media.php and managed to get into my very own custom function which accepts a "captionalign" argument.

To make use of, paste the below code to your theme's "function.php" file - this will help you to specify a choice inside your caption tag named captionalign. By setting this to right, left, or center, you are able to specify a per-caption text alignment. Departing the attribute may have the caption default to anything you have your default alignment as.

A good example of this being used:

[caption align="aligncenter" width="300" caption="My caption" captionalign="right"]
<a href="http://www.myawesomeblog.com/wp-content/uploads/2010/05/image.jpg">
<img title="My image" src="http://www.myawesomeblog.com/wp-content/uploads/2010/05/image.jpg-300x216.jpg" alt="My image" width="300" height="216" />
</a>
[/caption]

Here is the function:

add_shortcode('wp_caption', 'custom_img_caption_shortcode');
add_shortcode('caption', 'custom_img_caption_shortcode');

/**
 * The Caption shortcode.
 *
 * Allows a plugin to replace the content that would otherwise be returned. The
 * filter is 'img_caption_shortcode' and passes an empty string, the attr
 * parameter and the content parameter values.
 *
 * The supported attributes for the shortcode are 'id', 'align', 'width', and
 * 'caption'.
 *
 * @since 2.6.0
 *
 * @param array $attr Attributes attributed to the shortcode.
 * @param string $content Optional. Shortcode content.
 * @return string
 */
function custom_img_caption_shortcode($attr, $content = null) {

// Allow plugins/themes to override the default caption template.
$output = apply_filters('img_caption_shortcode', '', $attr, $content);
if ( $output != '' )
    return $output;

extract(shortcode_atts(array(
    'id'    => '',
    'align' => 'alignnone',
    'width' => '',
    'caption' => '',
    'captionalign' => ''
), $attr));

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

if ( $id ) $id = 'id="' . esc_attr($id) . '" ';

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

Hope that can help someone!

Asked using blogging platforms community site forum too, no response so most probably this is not an element of two.2.1