Julia released experimental support for arrays whose indexes don't start at 1 in Julia 0.5, October 2016.
The boundschecking feature was added in 2015, so at the time they wrote their code and examples, they were correct.
The documentation and review happened in December and January 2016/2017 when the non 1-based indexing was still experimental and very new, so I don't think this is as big a fail as you've made out either.
Yes, the documentation should have been updated when non-standard indexing was made non-experimental, and the reviewers should maybe have noted the new and experimental array indexing stuff, but it's only natural to miss some things.
That's fair enough! I was unaware of that history. But my point wasn't that the issue was "a big fail", it's that the GP was unfair in assigning the responsibility of that failure to "some newcomers [who] write code (and documentation) with this" while "the people who really know to handle these cases" are fine. The responsibility should have been on the people pushing for the experimental array indexing code to make it work safely with the existing usage of boundschecks that existed in the ecosystem and the existing documentation. It's a fundamental disagreement between whether the onus of code safety is on the user (who is responsible for understanding the totality of the libraries they're using and all of the ways they can fail) or on the programming language (for ensuring the stability and correctness of its code, documentation and ecosystem when making changes).
The boundschecking feature was added in 2015, so at the time they wrote their code and examples, they were correct.
The documentation and review happened in December and January 2016/2017 when the non 1-based indexing was still experimental and very new, so I don't think this is as big a fail as you've made out either.
Yes, the documentation should have been updated when non-standard indexing was made non-experimental, and the reviewers should maybe have noted the new and experimental array indexing stuff, but it's only natural to miss some things.