您不能为每个帖子创建主标记。标签是一种非海生分类法，根据定义，非海生分类法没有海生分类法，没有一个术语比其他术语更重要。

为了完成您的任务，大多数WP开发人员会建议您创建一些自定义字段来存储您的“主标签”，然后使用它来检索您的相关帖子。在你的函数中是这样的。php将构建自定义字段元盒：

/**
 * Generated by the WordPress Meta Box Generator at http://goo.gl/8nwllb

 */
class Custom_Meta_Box {
private $screens = array(
    \'post\',
);
private $fields = array(
    array(
        \'id\' => \'main-tag\',
        \'label\' => \'Main tag\',
        \'type\' => \'text\',
    ),
);

/**
 * Class construct method. Adds actions to their respective WordPress hooks.
 */
public function __construct() {
    add_action( \'add_meta_boxes\', array( $this, \'add_meta_boxes\' ) );
    add_action( \'save_post\', array( $this, \'save_post\' ) );
}

/**
 * Hooks into WordPress\' add_meta_boxes function.
 * Goes through screens (post types) and adds the meta box.
 */
public function add_meta_boxes() {
    foreach ( $this->screens as $screen ) {
        add_meta_box(
            \'main-tag\',
            __( \'Main Tag\', \'your-textdomain\' ),
            array( $this, \'add_meta_box_callback\' ),
            $screen,
            \'side\',
            \'default\'
        );
    }
}

/**
 * Generates the HTML for the meta box
 * 
 * @param object $post WordPress post object
 */
public function add_meta_box_callback( $post ) {
    wp_nonce_field( \'main_tag_data\', \'main_tag_nonce\' );
    echo \'Use this field to set the main tag:\';
    $this->generate_fields( $post );
}

/**
 * Generates the field\'s HTML for the meta box.
 */
public function generate_fields( $post ) {
    $output = \'\';
    foreach ( $this->fields as $field ) {
        $label = \'<label for="\' . $field[\'id\'] . \'">\' . $field[\'label\'] . \'</label>\';
        $db_value = get_post_meta( $post->ID, \'main_tag\', true );
        switch ( $field[\'type\'] ) {
            default:
                $input = sprintf(
                    \'<input id="%s" name="%s" type="%s" value="%s">\',
                    $field[\'id\'],
                    $field[\'id\'],
                    $field[\'type\'],
                    $db_value
                );
        }
        $output .= \'<p>\' . $label . \'<br>\' . $input . \'</p>\';
    }
    echo $output;
}

/**
 * Hooks into WordPress\' save_post function
 */
public function save_post( $post_id ) {
    if ( ! isset( $_POST[\'main_tag_nonce\'] ) )
        return $post_id;

    $nonce = $_POST[\'main_tag_nonce\'];
    if ( !wp_verify_nonce( $nonce, \'main_tag_data\' ) )
        return $post_id;

    if ( defined( \'DOING_AUTOSAVE\' ) && DOING_AUTOSAVE )
        return $post_id;

    foreach ( $this->fields as $field ) {
        if ( isset( $_POST[ $field[\'id\'] ] ) ) {
            switch ( $field[\'type\'] ) {
                case \'email\':
                    $_POST[ $field[\'id\'] ] = sanitize_email( $_POST[ $field[\'id\'] ] );
                    break;
                case \'text\':
                    $_POST[ $field[\'id\'] ] = sanitize_text_field( $_POST[ $field[\'id\'] ] );
                    break;
            }
            update_post_meta( $post_id, \'main_tag\', $_POST[ $field[\'id\'] ] );
        } else if ( $field[\'type\'] === \'checkbox\' ) {
            update_post_meta( $post_id, \'main_tag\', \'0\' );
        }
    }
}
}
new Custom_Meta_Box;

一旦有了自定义字段元盒，就应该用有效的标记slug（我建议slug优于名称或术语ID）填充它，并通过在single中进行此类查询来检索相关帖子。php：

$args = array(
    \'meta_key\'   => \'main_tag\',
    \'meta_value\' => get_post_meta($post->ID, \'main_tag\', true);
);
$query = new WP_Query( $args );