Regex case sensitivity workaround in accept.txt doesn't work as expected

[jrahal-mx]

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Environment

OS: macOS 13.4.1
Install Method: Homebrew
Vale Version: 3.7.1

Describe the bug / provide steps to reproduce it

In accept.txt, if I add [Oo]bservability per the example in the docs, Vale will accept observability and Observability.

I'd expect oBservability to trigger an alert because it doesn't match the pattern of:

• Case sensitively matching a single character in the list [Oo]
• Case sensitively matching bservability

Instead, it seems that Vale ignores casing on the rest of the string outside of Oo.

Do I need to build the regex differently to get it to match only lower-case bservability?