RE: [External] : Inspecting behaviour of `make-overlay', is this expected?

[Drew Adams]

> > XXXXXXXXXX
> > ^
> > | position 0 in buffer
> 
> Position 1.  Buffer positions start with 1.
> 
> Try (make-overlay 1 11).

You _can_ pass 0 to `make-overlay', but it
creates the overlay starting at position 1.

E.g. (make-overlay 0 10) creates an overlay
from the first position, 1, through the 9th
(as Eli mentioned).

As (elisp) `Managing Overlays' tells you:

 Function: make-overlay start end &optional buffer front-advance
           rear-advance
     This function creates and returns an overlay that belongs to BUFFER
     and ranges from START to END.  Both START and END must specify
     buffer positions; they may be integers or markers

You can use `overlay-start' and `overlay-end'
to see the limits of your overlay.