Boardview for the iPhone 5S, labelled as the WCDMA variant, in .bvr format at 270 KB. The 5S was built in several regional versions with different radio hardware, and this file targets the WCDMA model, so compare the radio section with your board before relying on it. In a viewer you can locate any component by reference, follow nets across the board and identify test points on power rails and connectors. It is a practical aid for tracing shorts, checking baseband related circuits and verifying continuity after rework.
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 @SMART_PHONE_SCHEMATICS. Enginerys does not host this file.
How to open a .bvr file
Text boardview from the BoardView R family of tools, seen for Lenovo, MSI and Clevo boards.