SpatialSeries.reference_frame doc only describes direction use case, not position

[ehennestad]

Summary

The doc string for SpatialSeries.reference_frame in nwb.behavior.yaml only describes the direction use case of SpatialSeries, leaving position users without guidance.

Current doc string

Description defining what exactly 'straight-ahead' means.

Problem

SpatialSeries is used for both direction data (e.g. gaze angle) and position data (e.g. animal location in an enclosure). The type-level doc correctly covers both with examples:

• Direction: "straight-ahead" as a pixel on a monitor
• Position: (0, 0) as the top-left corner of an enclosure

But reference_frame itself only mentions "straight-ahead", which is meaningless for position data. A user storing position coordinates has no schema guidance on how to describe their reference frame.

Proposed fix

Expand the reference_frame doc to cover both use cases, e.g.:

Description of the reference frame for the data. For position data, describe
the origin and orientation of the coordinate system (e.g. '(0, 0) is the
top-left corner of the enclosure, x increases rightward, y increases downward').
For direction data, describe what constitutes straight-ahead or zero angle
(e.g. 'straight-ahead is a pixel on a monitor at (512, 400)').

Optional: To avoid duplication, the main doc string could point to reference_frame dataset