add different behaviors for fragments
For example: I want to have one picture appear on screen, and then on the next "fragment," I want to replace that picture with another picture.
I don't want to go onto another slide, I just want to replace one picture with another. It would be perfectly fine if this picture just went above the old one; all I care about is that the audience sees one, and then sees another.
I can't figure out a clean way to do this with slid.es.

The described use case should be more straight forward in the new editor that was just launched into public beta. You’ll need to add two images, turn them both into fragments, and drag them on top of each other.
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brychanrobot commented
It is possible to create a stacked fragment by setting up the fragments and then moving them on top of each other. The problem is that it's kind of ugly in the editor, and changing an individual fragment requires you to separate them again, make the change, and then realign them. It would be fantastic if there was a way to more easily create and edit stacked fragments.
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Anonymous commented
The proposed solution does not fix overlap issues when images have transparency. There needs to be way to hide any previous images since not all images may conform to a standard rectangle.