It's actually surprisingly difficult to get this kind of thing right. It seems perfectly obvious in hindsight, but while you're designing, little details like this get missed.

When I started writing a spec for Concise Text Encoding [1], I figured it would take about 6 months to nail it down (yeah, right). Even now, 2 years later, I'm still making amendments to it because of various things I missed or got wrong. It's either something I happen to notice in one of my many, many re-reads, or something that another person notices after a few minutes reading it over, or something that comes up while I'm writing the reference implementation. Getting a spec right is a marathon affair.

[1] https://github.com/kstenerud/concise-encoding/blob/master/ct...