Which of the following options is correct regarding Placeholders?

A Placeholder is a feature in OutSystems that allows developers to create a designated area within a block or screen where content can be added dynamically when the block is instantiated. This enhances the flexibility of the user interface by letting developers design reusable blocks that can accept different content based on the specific needs of the context in which they are used. The key aspect of placeholders is that they serve as a reserved space, which gets populated at runtime rather than being a fixed element in the design.

This means that when you instantiate a block containing placeholders, the placeholders dynamically adapt to receive and display the intended content, thus allowing for more modular and maintainable code. The ability to use placeholders supports the creation of complex layouts while minimizing redundancy and maximizing reusability.

The other options don’t accurately represent how placeholders work. It's not mandatory to place at least one widget inside the placeholders when a block is instantiated; they can remain empty. Furthermore, while placeholders can indeed be added to both screens and blocks, there’s no restriction that limits the number of placeholders to just one per block; multiple placeholders can exist within a single block to allow for multiple areas of dynamic content placement.