In the context of Boomla, a hash is a unique identifier of an object.
A hash-based link mounts another volume by its hash. The mounted volume is part of the filesystem and the link can not break.
Modifying a volume mounted via a hash-based link causes hash change propagation in the linking volume.
File links are either hash-based or location-based.
The hash of a file is calculated from its properties, attributes, body and children. If a file changes, it will cause the hash of its parent file to be recalculated and so on upwards in the tree. This is called hash change propagation.
A package link is a file link mounting a package by its hash. The package link is a hash-based link: the mounted subtree becomes part of the website and remains there even if the original package website is removed.
package example.com 01ed8bb7a8ad5500c8885da1575f77068d0777606d