A child object can be prevented from being scaled when resizing its parent and be anchored to its parent in different ways. This ensures that designs can be presented in different layouts quickly and easily. As an example, you can nest caption strips within your picture frames, whose shape and caption text can be controlled with respect to anchoring and scaling.
Using constraints gives you the freedom to design without worrying that design rework will be adversely affected by unwanted object rescaling. By controlling selectively which objects will/won't be scaled and anchored, your design will always respond correctly to scaling.
Constraints only work in parent - child object relationships, i.e. where a parent object (container) contains nested content. A child object's scaling and anchoring is always in relation with its parent container. For example, a page and a child text frame, etc.
By default, nested content will scale when its container is resized. A child object is not anchored by default.
To prevent a child object losing its aspect ratio when its parent is scaled disproportionately, you can set it to Min-Fit or Max-Fit.
Min-Fit—when the parent object is resized disproportionately, the child object may scale so it always fits within its parent object (if unanchored). Use on text to ensure it always fully displays.
Max-Fit—when the parent object is resized disproportionately, the child object may scale. The child object can become bigger than its parent object, potentially clipping content from view. Using a web banner mockup as an example, a child object (e.g., an image) will always fully fill the containing banner area (avoiding white letterboxing) but may be subject to clipping.In both cases, if the parent object is resized proportionately, the child object will also scale proportionally.