This is a variant of SilverStripe FocusPoint field, allowing you to use a similar interface for setting x and y coords on a DataObject by clicking on an image.
Not documented currently because I wasn't sure if it would be used outside of one or two projects 😄. If you're wanting to use it and need some help, please raise an issue.
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Please also feel free to get in touch if you want to hire the maintainer to develop a new feature, or discuss another opportunity.