article body

add_action( 'rank_math/vars/register_extra_replacements', function(){
    rank_math_register_var_replacement(
        'articleBody', [
            'name'        => esc_html__( 'Article Body', 'rank-math' ),
            'description' => esc_html__( 'Output the content.', 'rank-math' ),
            'variable'    => 'articleBody',
            'example'     => articleBody_callback(),
        ],
        'articleBody_callback'
    );
});

function articleBody_callback() {
    $body = wp_strip_all_tags(get_the_content());
    return substr($body, 0, 400);
}