Document TIFF tags used by imagej

TIFF tags used by ImageJ are not documented.
Here is my use case. Imagej has an awesome overlay feature. I would like to use imagej to display an image with non-destructive overlays showing the results of object detection from the image. The detection is done by my own program. I would like to be able to write TIFF files with imagej-specific tags describing the overlays. I would like in particular to create point overlays with subpixel (float) positioning. Without the documentation of the tags, I have to glean their meaning from the source code, but then I cannot be sure the format won't change.

Start by examining the ImageJ source code that defines the TIFF tags, focusing on tags for overlays and point positions. Document the tag meanings and the format for subpixel coordinates, including whether the documented format is stable enough for external TIFF writers.

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