The 'instructions' field in 'manifest.custom-field-definitions' doesn't do what the documentation says

The Custom Fields documentation says:

instructions : Optional block of remarkup text which will appear above the control when rendered on the edit view.

However, this text doesn’t seem to appear in any edit/create form where the field is used. In fact, if I put my desired instructions into each of the description, caption, and instructions fields, the only text I can get to show up is the is the caption text, which doesn’t render ReMarkup.

I would like to use this field to describe the uses of the options of a select field. E.g., how to use different severities.

Is there some way to force the instructions to be visible?