Wordpress: Format wp_head() Output as HTML 4.01 Transitional

31 March 2012

While I’m no longer as much of a purist as I used to be, whenever I’m tasked with writing HTML, I usually go to great lengths to make sure that it is valid. For academic reasons beyond the scope of this artcle, my preferred DOCTYPE is still HTML 4.01 Transitional, and I almost always code - and validate my code - to that standard.

Having been doing a lot of Wordpress work recently, however, I’ve discovered an annoying Wordpress quirk that can make it difficult to produce valid HTML 4.01 Transitional code: the wp_head() method outputs markup formatted for XHTML, and thus, its output will register as invalid when validated against the HTML 4.01 Transitional DOCTYPE.

This problem is easily solved, however. Rather than calling wp_head() within a theme directly, I’ve just started using a modified function instead:

<?php
/**
 * Returns wp_head() formatted for an HTML 4.01 transitional DOCTYPE
 * 
 * @return string $html
 */
function wp_head_html_401(){
    ob_start();
    wp_head();
    $html = ob_get_clean();
    $html = str_replace('/>', '>', $html);
    return $html;
}

The above function can be copied into your functions.php file, and simply invoked in your header.php file. (Remember to echo the output of this function in your header file, since, unlike the original wp_head() function, this function returns, rather than echoes, its output. I’m generally not a fan of functions which echo their output by default.)

What this code is doing should be fairly obvious: we’re starting an output buffer, running wp_head(), and doing a simple string substitution on the output. We are thus able to generate markup that’s compliant with our desired DOCTYPE.