This post is another effort of mine in understanding the core of WordPress. Hopefully at the end of this post, you’ll gain something about. My goal is to have better understanding of the way WP render particular parts of the website by using the filters.
Dive into the header.php file of WP theme
I’m using store front theme on my local dev site. However, you’ll encounter the same layout/code in any other themes.
This is the part of the code that renders the header
<head> <meta charset="<?php bloginfo( 'charset' ); ?>"> <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=2.0"> <link rel="profile" href="http://gmpg.org/xfn/11"> <link rel="pingback" href="<?php bloginfo( 'pingback_url' ); ?>"> <?php wp_head(); ?> </head>
As you can see, there is no title tag. However, there is a piece of PHP code that generates the title and other stuffs. That’s wp_head()
Dive into wp_head function
The code for wp_head is surprisingly simple:
function wp_head() {
/**
* Prints scripts or data in the head tag on the front end.
*
* @since 1.5.0
*/
do_action( 'wp_head' );
}
It calls another function called do_action with the parameter ‘wp_head’. I hope you have, at least a vague understanding of how filters and actions work in WordPress.
Now, we need to know where the title’s filters are added to the wp_head hook. With the help of PhpStorm, I was able to locate this part:
add_action( 'wp_head', '_wp_render_title_tag', 1 );
As you can see, there is a function that responsible for rendering the title called ‘_wp_render_title_tag’. Let’s see what does it do:
function _wp_render_title_tag() {
if ( ! current_theme_supports( 'title-tag' ) ) {
return;
}
echo '<title>' . wp_get_document_title() . '</title>' . "\n";
}
Once again, the function is very short since it calls other functions. Our next step would be investigating the function ‘wp_get_document_title’
function wp_get_document_title() {
/**
* Filters the document title before it is generated.
*
* Passing a non-empty value will short-circuit wp_get_document_title(),
* returning that value instead.
*
* @since 4.4.0
*
* @param string $title The document title. Default empty string.
*/
$title = apply_filters( 'pre_get_document_title', '' );
if ( ! empty( $title ) ) {
return $title;
}
global $page, $paged;
$title = array(
'title' => '',
);
// If it's a 404 page, use a "Page not found" title.
if ( is_404() ) {
$title['title'] = __( 'Page not found' );
// If it's a search, use a dynamic search results title.
} elseif ( is_search() ) {
/* translators: %s: search phrase */
$title['title'] = sprintf( __( 'Search Results for “%s”' ), get_search_query() );
// If on the front page, use the site title.
} elseif ( is_front_page() ) {
$title['title'] = get_bloginfo( 'name', 'display' );
// If on a post type archive, use the post type archive title.
} elseif ( is_post_type_archive() ) {
$title['title'] = post_type_archive_title( '', false );
// If on a taxonomy archive, use the term title.
} elseif ( is_tax() ) {
$title['title'] = single_term_title( '', false );
/*
* If we're on the blog page that is not the homepage or
* a single post of any post type, use the post title.
*/
} elseif ( is_home() || is_singular() ) {
$title['title'] = single_post_title( '', false );
// If on a category or tag archive, use the term title.
} elseif ( is_category() || is_tag() ) {
$title['title'] = single_term_title( '', false );
// If on an author archive, use the author's display name.
} elseif ( is_author() && $author = get_queried_object() ) {
$title['title'] = $author->display_name;
// If it's a date archive, use the date as the title.
} elseif ( is_year() ) {
$title['title'] = get_the_date( _x( 'Y', 'yearly archives date format' ) );
} elseif ( is_month() ) {
$title['title'] = get_the_date( _x( 'F Y', 'monthly archives date format' ) );
} elseif ( is_day() ) {
$title['title'] = get_the_date();
}
// Add a page number if necessary.
if ( ( $paged >= 2 || $page >= 2 ) && ! is_404() ) {
$title['page'] = sprintf( __( 'Page %s' ), max( $paged, $page ) );
}
// Append the description or site title to give context.
if ( is_front_page() ) {
$title['tagline'] = get_bloginfo( 'description', 'display' );
} else {
$title['site'] = get_bloginfo( 'name', 'display' );
}
/**
* Filters the separator for the document title.
*
* @since 4.4.0
*
* @param string $sep Document title separator. Default '-'.
*/
$sep = apply_filters( 'document_title_separator', '-' );
/**
* Filters the parts of the document title.
*
* @since 4.4.0
*
* @param array $title {
* The document title parts.
*
* @type string $title Title of the viewed page.
* @type string $page Optional. Page number if paginated.
* @type string $tagline Optional. Site description when on home page.
* @type string $site Optional. Site title when not on home page.
* }
*/
$title = apply_filters( 'document_title_parts', $title );
$title = implode( " $sep ", array_filter( $title ) );
$title = wptexturize( $title );
$title = convert_chars( $title );
$title = esc_html( $title );
$title = capital_P_dangit( $title );
return $title;
}
This function is quite lengthy since it does all of jobs of generating the title. You can also see that, while the title tag is a small part of the document, this function isn’t a simple one at all. It’s partly because WordPress offers so much flexibility for developers to modify the titles and other parts of the content.
As you read through the code, you’ll see that this function checks for what kind of page it’s currently on (whether it’s a homepage/archive page…) and render the title for such pages accordingly.
You may have some confusions regarding the apply_filters part. That’s the topic of another post which I’m going to write shortly.