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The reference point of a frame is configurable on document and frame level (cascading: frame overrules document setting)configured at the Frame Location panel
When you choose the top-left corner as the reference point, all coordinates (X, Y, width, Height, Rotation, Skew, ...) will refer off that point.
In the picture 1, you see the X and Y of the frame, is 0, meaning it aligns to the top left of the document.
When we now change the reference point to the top right, the coordinates will be recalculated.
Important: the frame will not change, but the relative position according to the reference point will change.
If you would now change the X position to 0, then the top-right corner will align with the top-left corder of the document, since the frame reference point is top-right.
The frame’s reference point defines how the frame will behave if the width, height, scale, x or y values are modified through the frame location panel, actions or dynamic layout functions. Changing these properties inline by using the frame handles on the document canvas is not affected by this setting.