An archive for the original Xiaomi Mi 1, in RAR format of about 518 KB. Nothing beyond the model is given in the name: no board number, revision or content type. Its size is in line with the separate Mi 1 schematic ZIP, so it probably contains similar circuit pages, though extraction will confirm. Repairers use such schematics to trace supply rails, test charging and battery circuits, and locate parts on a shorted net. Check the PCB markings against the sheet headers before relying on the drawings.
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 @cyberlanelectonik. 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.