Sometimes it is useful to "macro process" a parameter before using it in the replacement part. This is particularly important when using certain built-in macros.

For prescan to occur, the parameter must be specified in the template with two dollar signs instead of one, and the actual parameter must begin with an "at" sign (@), which is stripped off.

An example of prescan follows:

For example, the string:

is replaced by:

However, the entry:

results in:

For another example of the use of prescan, see Special Macros.