What must each macro include to function properly?

For a macro to function properly, it is essential for it to have at least one input parameter. Input parameters are the variables that a macro uses to perform its tasks. They allow users to pass specific values into the macro, thus enabling it to operate dynamically based on the input provided. Without an input parameter, the macro would lack the necessary information to execute its predefined operations, rendering it ineffective or causing errors in execution.

In a macro-writing context, input parameters can be seen as a way to customize the behavior of the macro for different use cases. They ensure that the macro can adapt to different scenarios based on the data or instructions it receives upon execution.

The other options, while relevant in certain contexts, do not are necessary requirements for the basic functioning of a macro. For instance, a description of its output, although useful for documentation purposes, is not strictly required for operation. Similarly, assigning a designated user for execution or specifying a usage limit are not foundational aspects of a macro's functionality. Hence, the key element for proper operation is the inclusion of at least one input parameter.