#existing is e.g. implicitly used by //replace with only one argument. It's basically a "not air". It is also used in #air but negated, so supporting InverseMasks were the original mask can be vectorized is simple and useful.
### Submitter Checklist
- [x] Make sure you are opening from a topic branch (**/feature/fix/docs/ branch** (right side)) and not your main branch.
- [x] Ensure that the pull request title represents the desired changelog entry.
- [x] New public fields and methods are annotated with `@since TODO`.
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Overview
Description
#existingis e.g. implicitly used by//replacewith only one argument. It's basically a "not air". It is also used in#airbut negated, so supportingInverseMasks were the original mask can be vectorized is simple and useful.