B. Terminal Monitor : Terminal Monitor Macros : More on Parameters
 
More on Parameters
Parameters need not be limited to the word that follows. For example, in the template descriptor for {define},
{define; $t; $r}
the $t parameter ends at the first semicolon, and the $r parameter ends at the first right curly brace. In general, the character that follows the parameter specifier terminates the parameter. If this character is a space, tab, newline or the end of the template, one word or one string appropriately surrounded (' and ') is collected.
There is one important exception to this general rule: because system macros (described below) are always surrounded by curly braces, the macro processor requires them to be properly nested. Thus, in the macro definition:
{define; x; {type enter dat-}}
the first right curly brace closes the type rather than the define.