Note: This is a work in progress and many formatting issues have been fixed. Read more about the project on the home page.
A handler can receive values (called parameters) and use them as it runs. You represent each value with a parameter variable. A parameter variable always follows the handler name in a comma-separated list.
For example, when running the following mouseUp handler, HyperCard calls sayMessage with two values, "red" and "apple". It then binds these values to the parameter variables color and fruit in the sayMessage handler.
You can use the variables color and fruit anywhere inside the handler. When HyperCard sees them, it uses the values currently bound to them. (The variables remain bound only while the handler runs.)