Beginning of CLI interface + protection against infinite recursion.

README.md

@@ -6,3 +6,19 @@ Blender Asset Tracer, a.k.a. BAT🦇, is the replacement of [BAM](https://develo
 and [blender-file](https://developer.blender.org/source/blender-file/)
 
 Development is driven by choices explained in [T54125](https://developer.blender.org/T54125).
+
+
+## Paths
+
+There are two object types used to represent file paths. Those are strictly separated.
+
+1. `bpathlib.BlendPath` represents a path as stored in a blend file. It consists of bytes, and is
+   blendfile-relative when it starts with `//`. It can represent any path from any OS Blender
+   supports, and as such should be used carefully.
+2. `pathlib.Path` represents an actual path, possibly on the local filesystem of the computer
+   running BAT. Any filesystem operation (such as checking whether it exists) must be done using a
+   `pathlib.Path`.
+
+When it is necessary to interpret a `bpathlib.BlendPath` as a real path instead of a sequence of
+bytes, BAT assumes it is encoded as UTF-8. This is not necessarily true, and possibly using the
+local filesystem encoding might be better, but that is also no guarantee of correctness.