Bethesda Game Studios introduced the PPJ schema with the Papyrus Compiler for FO4. The TES5 and SSE compilers do not support Papyrus Projects.
Pyro, however, brings Papyrus Projects to TES5 and SSE, and supports the entire official schema in addition to a ton of new features unique to Pyro.
Note: The Asm attribute of the PapyrusProject node is ignored by Pyro. The Papyrus Compiler uses this attribute to call the Papyrus Assembler but generating assembly files for Papyrus scripts is out-of-scope for Pyro.
See: Pyro Project Schema
For information about document structure, type constraints, and other rules, refer to the XSD directly.
See: Pyro Project XML Schema Definition