This is the world save data file. The associated file dynidx0.mul is its index.
By default this file cannot be written to, but analysis of the exe has shown that a function exists which can write back the data file. UoDemo+, Publish 8 has been created and added the SAVEDYNAMIC0 option so you can enable this hidden save functionality.
This file is structured as a nested object list.
Each top level entity in the file begins with @=<type> and ends with @end Nested Entities do not require @end
Identified types (and guesses):
B=Bulletin Board C=Container D=Dynamic Item??: (Book,Board,Ingot,Small Fish,Rope) E=Chunk Egg G=Guard N=NPC/Creature P=Player S=Shopkeeper W=Wearable (Weapon,Armor) Z=Item
@=P <propery>=<value> ... @=[D|C|E] <propery>=<value> ... @end