[vim/vim] pattern.txt says `[:upper:]` and `[:lower:]` respect `ignorecase`, but they don't (Issue #19230)

taylor.fish

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Jan 21, 2026, 2:31:43 AM (2 days ago) Jan 21

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taylordotfish created an issue (vim/vim#19230)

Steps to reproduce

Open :help [:upper:].
Observe that the description says uppercase letters (all letters when 'ignorecase' is used).
Run :set ignorecase.
Run :echo 'a' =~ '[[:upper:]]'.
Observe that the pattern did not match.

The above steps can be repeated for [:lower:], substituting 'A' for 'a' in step 4.

Expected behaviour

I expected the documentation not to say that these character classes match all letters when ignorecase is used. This would make it consistent with :help /ignorecase, which states Note that 'ignorecase', "\c" and "\C" are not used for the character classes., as well as with the actual behavior of the character classes in practice.

Version of Vim

9.1.2101

Environment

Operating system: Debian 13
Terminal: rxvt-unicode v9.31
Value of $TERM: tmux-256color
Shell: GNU bash, version 5.2.37(1)-release

Logs and stack traces

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Christian Brabandt

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Jan 21, 2026, 3:11:51 PM (2 days ago) Jan 21

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chrisbra left a comment (vim/vim#19230)

That's is however correct behavior when matching text in the buffer using the backtracking regexp engine (e.g. after :set regexpengine=1), but when using an expression operator =~ it is always ignored. Strange

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taylor.fish

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Jan 22, 2026, 8:18:36 AM (yesterday) Jan 22

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taylordotfish left a comment (vim/vim#19230)

Interesting, for me, after :set regexpengine=1, the behavior of =~ updates too. :set ic re=1 | echo 'a' =~ '[[:upper:]]' prints 1.

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Christian Brabandt

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Jan 22, 2026, 4:12:18 PM (20 hours ago) Jan 22

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chrisbra left a comment (vim/vim#19230)

Yeah, I am unsure if we should just document this inconsistency and how. Any idea for a doc patch?
I had a quick look yesterday at the backtracking code, but did not find where this ignorecase setting was applied.