The syntax for event specifications and modifiers is keyword driven and based on ksh conventions. Everything is split into words delimited by spaces.
Expressions can have spaces embedded in them, causing ambiguous situations. For example, consider the following two commands:
when a -temp when a-temp
In the first example, even though the application might have a variable named temp, the dbx parser resolves the event specification in favor of –temp being a modifier. In the second example, a-temp is collectively passed to a language-specific expression parser. If no variables are named a and temp, an error occurs. Use parentheses to force parsing.