Within

A spatial object is considered within another spatial object when all its points are inside the other object's interior. Thus, if a point or linestring only exists along a polygon's boundary, it is not considered within the polygon. The polygon boundary is not part of its interior.

If a point is on a linestring, it is considered within the linestring. The interior of a linestring is all the points along the linestring, except the start and end points.

Within(a, b) is spatially equivalent to contains(b, a).