How does SQL STBuffer measure distance around polygons?

How does the STBuffer function measure distances around a polygon?

I am looking at the expression:

select SP_GEOMETRY.STBuffer(100)

and wondering how the 100-meter buffer is calculated around the geometry of polygons.

e.g., is it from the centre of the polygon? or does the buffer start from the edges of the polygon?

I am struggling to find helpful documentation on this so if you have any links let me know!

I am wondering because the function is trying to pick up boundaries which are within 100m from each other, but when running the function, not all the properties within 100m are being selected.

Based on the documentation:

It would return a buffer around the edges of the geometry object. Although that doesn't seem to be clearly stated in that link. There are examples in there that return polygon buffers based on line objects, and some other polygon types that wouldn't be simply from the center/centroid.

Edit: confirmed, if you try this and look at the Spatial results in SSMS:

DECLARE @g geometry= 'LINESTRING(3 4, 8 11)'; 
SELECT @g.STBuffer(2)--.ToString();