Here at MDN, we try to avoid outright deleting content that might be useful to people targeting legacy platforms, operating systems, and browsers. Perhaps your target audience is people that are using older hardware, for example, and can't upgrade to the latest and greatest browsers. Or for "reasons," your company is required to use very old software and you need to build Web content that runs on that software. Or perhaps you're just curious about the history of an obsolete feature or API, and how it worked.
There are many reasons older documentation can be useful. So, we've established this area into which we can archive older documentation. Material in this Archived content zone should not be used for building new Web sites or apps for modern browsers. It's here for historical reference only.
Note to writers: We need to try to keep the subpages here organized instead of all dumped into one large folder. Try to create subtrees for categories of material. Also, only move pages here that are extremely obsolete. If anyone might realistically need the information in a living product, it may not be appropriate to move it here. In general, it may be best to discuss it in the MDN Web Docs chat room before moving content here.