I'll admit, to me the point that the author considers 90% is where I consider 99%.
IMO, getting from 90% (it works and does the right thing with any valid input) to 99% involves things like
- paying down all technical debt
- handling malformed or adversarial inputs, including all edge-cases, "reasonably"
- better documentation; tutorials, how-tos, explainers, and references. In multiple formats (don't forget your `man` page).
- checking for low-hanging perf/memory wins.
- interface polish. Is there a long-running operation that might benefit from a progress bar? Or some other indicators which aren't strictly necessary, but would help users model of the state of the program?
> What are some common activities to go from 90% to 100%?
To the list I'll add
- 100% coverage
- rewrite it in Rust (ha ha)