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Primary Term

What is a primary term?​

A post can belong to many terms in a taxonomy. For example, a post can be in two categories, or a product can be in two product categories. When a post has no primary term, the plugin uses the first term for the breadcrumb and the permalink. That term is not always the most important one.

The primary term is the term that you mark as most important for the post.

Why do you need a primary term?​

When a post has many terms, search engines do not know which one is the main topic of the post. This gives weaker SEO results:

  • The breadcrumb trail shows the wrong term.
  • The permalink can change when you add or remove a term.
  • The site hierarchy looks unclear.

A primary term fixes these problems. It makes the breadcrumb and the permalink stable for the post. The post keeps the same term even when its term set changes. This gives search engines a clear signal about the main topic of the post.

Setting a primary term​

You set the primary term in the post editor. The way you do it depends on the editor that you use.

Block editor​

In the block editor, select two or more terms in the taxonomy panel. The plugin then shows a "Primary" dropdown below the list of terms. Pick one term to set it as the primary term.

Set a primary term in the block editor

When you select only one term, the plugin uses it automatically. So the dropdown does not appear.

Classic editor​

In the classic editor, check the terms that you want for the post. When you select two or more terms, the plugin shows a link next to each checked one. Click the "Set primary" link to mark that term as the primary one. The active primary term shows the "Primary" label.

Set a primary term in the classic editor

Automation

When you do not set a primary term, the plugin keeps the default behavior. It uses the first term for the breadcrumb and the permalink. The primary term only changes the output when you choose it.

The primary term changes the post permalink when the permalink structure contains a term placeholder. A term placeholder has the form %taxonomy_slug%. It is the slug of the taxonomy wrapped in % characters.

For example, the placeholder for the category taxonomy is %category%. The placeholder for the product_cat taxonomy is %product_cat%.

By default, Slim SEO does the permalink rewrite for two post types:

  • The post type, which uses the category taxonomy and the %category% placeholder.
  • The WooCommerce product type, which uses the product_cat taxonomy and the %product_cat% placeholder.

For the post type, Slim SEO reads the structure from the global permalink structure. For the product type, it reads the structure from the WooCommerce product permalink settings.

When the post has a primary term, the plugin replaces the placeholder in the permalink with that term. For a hierarchical taxonomy, the permalink also includes the parent terms.

The slim_seo_primary_term_rewrite filter lets you extend the permalink rewrite to other post types. The filter receives an array. Each post type in the array has two values:

  • taxonomy: the taxonomy that provides the primary term.
  • structure: the permalink structure of that post type. It is the structure that contains the term placeholder for that taxonomy.

For example, a custom post type named book uses a genre taxonomy. The permalink structure of the book post type contains the %genre% placeholder. The code below adds the permalink rewrite for the book post type:

add_filter( 'slim_seo_primary_term_rewrite', function( $data ) {
	$data['book'] = [
		'taxonomy'  => 'genre',
		'structure' => '/books/%genre%/%postname%/',
	];
	return $data;
} );