我已经查看了源代码，不幸的是，我没有找到一种不保存信息就传递信息的好方法。这太糟糕了，时间太长了，因为这真的不是什么需要挽救的事情。

解决方法是启用PHP Sessions 将以下内容放在functions.php:

    if (!session_id()) {
        session_start();
    }

    $_SESSION[ \'your-key\' ] = \'your-value\';

    function wpse_154330_attachment_fields_to_edit( $form_fields, $post ) {
        $current_screen = get_current_screen();
        // we are not saving, so no need to show the field on the attachment page
        if ( $current_screen->id == \'attachment\' ) {
            return $form_fields;
        }
        $form_fields[\'fancyboxGroup\'] = array(
            \'label\' => \'fancybox group\',
            \'input\' => \'text\',
            \'value\' => \'\', // leave the value empty
            \'helps\' => \'use this to group images in fancybox\',
        );
        return $form_fields;
    }
    add_filter(
        \'attachment_fields_to_edit\',
        \'wpse_154330_attachment_fields_to_edit\',
        10,
        2
    );

    function wpse154330_save_attachment_field( $post, $attachment ) {
        // we\'re only setting up the variable, not changing anything else
        if ( isset( $attachment[ \'fancyboxGroup\' ] ) {
            $_SESSION[ \'fancyboxGroup\' ] = $attachment[ \'fancyboxGroup\' ];
        }
        return $post;
    }
    add_filter(
        \'attachment_fields_to_save\',
        \'wpse154330_save_attachment_field\',
        10,
        2
    );

    function wpse154330_image_send_to_editor(
        $html,
        $id,
        $caption,
        $title,
        $align,
        $url,
        $size,
        $alt = \'\'
    ) {
        // no need to modify the output, if no fancybox group is given
        if (
            empty( $_SESSION[ \'fancyboxGroup\' ] )
            || ! isset( $_SESSION[ \'fancyboxGroup\' ] )
        ) {
            return $html;
        }
        $classes = \'fancybox\';
        if ( preg_match( \'/<a.*? class=".*?">/\', $html ) ) {
            $html = preg_replace(
                \'/(<a.*? class=".*?)(".*?>)/\',
                \'$1 \' . $classes . \'$2\',
                $html
            );
        } else {
            $html = preg_replace(
                \'/(<a.*?)>/\',
                \'$1 class="\'
                    . $classes
                    . \'" data-fancybox-group="\'
                    . $_SESSION[ \'fancyboxGroup\' ]
                    . \'" >\',
                $html
            );
        }
        unset( $_SESSION[ \'fancyboxGroup\' ] );
        return $html;
    }
    add_filter(
        \'image_send_to_editor\',
        \'wpse154330_image_send_to_editor\',
        10,
        8
    );