The literal meaning of scale and aspect in the Contentmode of UIView

Scale means: Scaling, appearing in Contentmode, is about changing the size of the graph.
Aspect means that the aspect ratio, in the contentmode meaning is to maintain the aspect ratio of the graph, keep the picture not deformed.

Scale aspect Fill: while maintaining the aspect ratio (aspect), zoom the picture (scales) so that the picture fills the container (fill).
Scale aspect Fit: while maintaining the aspect ratio (aspect), zoom the picture (scales) so that the picture appears inside the container (FIT).
Scale to fill: scales the picture so that the picture fills the container. Because there is no aspect, so it is not to maintain the aspect ratio.

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The literal meaning of scale and aspect in the Contentmode of UIView