Adobe InDesign - Manual (Page 212)

Object-based
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Liquid page rules: Guide-based
You can specify liquid behavior for size and location relative to the page edge for each object, either fixed or relative.
Each side of an object's bounding box or frame can either be fixed, or relative to its corresponding page edge. For example, the left side of
the frame can have a relationship only with the left edge of the page.
The height and width can either be fixed, or resizable relative to the page.
Watch this video on Applying object-based Liquid Layout rules .
Liquid page rules: Object-based
Alternate layouts
Use Alternate Layouts if you require different page sizes for print or digital publishing within the same document. You can use it to create different
sizes of a print advertisement. Or to design the horizontal and vertical layouts for devices such as the Apple iPad or Android tablets.
Alternate layouts and Pages panel
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