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filter is not described

post_link_category filter-hook . WP 3.5.0

Filters the category that gets used in the %category% permalink token.

Usage

add_filter( 'post_link_category', 'filter_function_name_604', 10, 3 );
function filter_function_name_604( $cat, $cats, $post ){
	// filter...

	return $cat;
}
$cat(WP_Term)
The category to use in the permalink.
$cats(array)
Array of all categories (WP_Term objects) associated with the post.
$post(WP_Post)
The post in question.

Where the hook is called

get_permalink()
post_link_category
wp-includes/link-template.php 185
$category_object = apply_filters( 'post_link_category', $cats[0], $cats, $post );

Where the hook is used (in WP core)

Does not used.