Change Request: Preserve the original casing of selectors in `no-duplicate-keyframe-selectors` error messages

[KumJungMin]

Environment

ESLint version: 10.8.0
@eslint/css version: ^2.0.0
Node version: v22.18.0
npm version: v10.9.3
Operating System: darwin 24.6.0

What problem do you want to solve?

• no-duplicate-keyframe-selectors correctly detects duplicate selectors regardless of casing, but its error messages display the selector in lowercase rather than as written.

/* eslint css/no-duplicate-keyframe-selectors: "error" */

@keyframes test {
  from {
    opacity: 0;
  }
  to {
    opacity: 1;
  }
  TO {
    opacity: 2;
  }
}

• The current error message is:

Unexpected duplicate selector 'to' found within keyframe block.

• The error location points to TO, but the message displays to.
• Preserving the reported selector’s original casing could make it easier to match the message to the code.
• The same plugin’s prefer-logical-properties rule preserves the original casing in the following examples: StackBlitz reproduction.

/* eslint css/prefer-logical-properties: "error" */

.example {
  MARGIN-LEFT: 16PX;
  text-align: RIGHT;
}

Expected logical property 'margin-inline-start' instead of 'MARGIN-LEFT'.
Expected logical value 'end' instead of 'RIGHT'.

What do you think is the correct solution?

• I’d suggest keeping the value used for duplicate detection separate from the value displayed in the error message, so the message preserves the reported selector’s original casing.
• The expected message for the example above would be:

Unexpected duplicate selector 'TO' found within keyframe block.

Participation

• I am willing to submit a pull request for this change.

AI acknowledgment

• I did not use AI to generate this issue report.
• (If the above is not checked) I have reviewed the AI-generated content before submitting.

Additional comments

Disclosure: I'm a participant of open source contribution program OSSCA