查看呈现搜索框的WordPress核心代码后：

/**
 * Displays the search box.
 *
 * @since 4.6.0
 *
 * @param string $text     The \'submit\' button label.
 * @param string $input_id ID attribute value for the search input field.
 */
public function search_box( $text, $input_id ) {
    if ( empty( $_REQUEST[\'s\'] ) && ! $this->has_items() ) {
        return;
    }

    $input_id = $input_id . \'-search-input\';

    if ( ! empty( $_REQUEST[\'orderby\'] ) ) {
        echo \'<input type="hidden" name="orderby" value="\' . esc_attr( $_REQUEST[\'orderby\'] ) . \'" />\';
    }
    if ( ! empty( $_REQUEST[\'order\'] ) ) {
        echo \'<input type="hidden" name="order" value="\' . esc_attr( $_REQUEST[\'order\'] ) . \'" />\';
    }
    ?>
    <p class="search-box">
        <label class="screen-reader-text" for="<?php echo esc_attr( $input_id ); ?>"><?php echo $text; ?>:</label>
        <input type="search" id="<?php echo esc_attr( $input_id ); ?>" class="wp-filter-search" name="s" value="<?php _admin_search_query(); ?>" placeholder="<?php esc_attr_e( \'Search installed plugins...\' ); ?>"/>
        <?php submit_button( $text, \'hide-if-js\', \'\', false, array( \'id\' => \'search-submit\' ) ); ?>
    </p>
    <?php
}