When Interchange creates a user session, it also initializes the scratch space (also referred to as the scratchpad) to hold various variables which are valid throughout the session.

By default, the scratch space is created empty. You can define default scratch variables and their values using ScratchDefault.

Once defined, a scratch variable will exist either until it is explicitly deleted (most probably using [scratchd] tag) or the session ends. The exception are so-called "temp" variables, which are normal scratch variables (they live in the scratch space), but are automatically deleted when page processing ends. You can use them for saving intermediate results that you calculate and display, and then want Interchange to automatically forget.

The catalog programmer has complete control over the scratch variables. The following tags manipulate the scratch space: [set], [seti], [tmp], [tmpn], [scratch] and [scratchd].

Here's a complete list of ways to set scratch variables.

In ITL:

In embedded Perl:

In GlobalSub code or usertags:

Here's a complete list of ways to get scratch variables.

In ITL:

In embedded Perl:

In GlobalSub code or usertags:

One other predefined use for scratch variables is to hold form processing code (code that is executed on users' form submission). See the [button] tag for examples.