Apple iPhone X repair archive, a 5.99 MB RAR file whose name mentions nothing besides the model. The actual contents, possibly schematics or a boardview for the stacked logic board, should be verified once unpacked. Because the iPhone X uses a two-layer sandwich board, documentation is especially useful for finding which layer a component or rail sits on, tracing interposer connections and locating test points. Make sure the board markings match the documents before using component references or expected voltages for diagnosis.
The button opens the matching file on RM Schematics, or a source page if it is not catalogued there yet. The original attachment is from @schematicslaptop. Enginerys does not host this file.
How to open a .rar file
Compressed archive — the usual wrapper for a schematic + boardview pair or a BIOS + EC set.