When the mp parameter in the URL is set to debug (i.e., mp=debug), it prevents the loading of timelines on the page. This is a feature primarily used for troubleshooting purposes.
When the mp parameter is set to preview in the URL (i.e., mp=preview), it unlocks the ability to load all timelines on the page, even those that are usually hidden. This feature lets you sneak a peek at all the animations on the page, without letting the regular users see them.
When the mp parameter in the URL is set to a specific number or a series of numbers separated by commas or dashes (i.e., mp=number, mp=number,number, or mp=number-number), it enables the preview of hidden timelines associated with those specific database IDs. Visible timelines will continue to be displayed as usual. This feature allows for selective viewing of specific timelines on the page.