public TileCategoryFrameMembership(
	int nFrameSequenceCount,
	params TileFrameMembership[] membership
)

The membership parameter is only a temporary object used in the process of constructing this object and is discarded when construction is complete. This is done to abbreviate the code that constructs these memberships since the number of distinct categories in which the tile's various frames are members is usually low, but there may be many distinct frames that are included in each category. This information is converted to a more optimal format during construction, which allows the code to determine if a frame is in a category without doing any searching. So the original membership data is no longer required.