Position of docstrings for union tags is strange

[AiOO]

When I want to add some comment about rectangle,

union shape
    = rectangle (point upper-left, point lower-right)
    # Information about a rectangle
    | circle (point origin, offset radius)
    ;

expected postion should be

union shape
    = rectangle (
        # Information about a rectangle
        point upper-left,
        point lower-right
    )
    | circle (point origin, offset radius)
    ;

but I have to add it like below.

union shape
    = rectangle (point upper-left, point lower-right)
    # Information about a rectangle
    | circle (point origin, offset radius)
    ;