keywords-exists

Used in [Conditional compilation] to tell a conditionalif statement to test whether a conditional variable exists or not rather that its value. The identifier for the variable in question must immediately follow the exists keyword. Unlike the not operator, exists can't take an expression as a parameter. The parameter must be an identifier. If the identifier wasn't preceded by exists, the compiler must issue an error if it can't find the symbol. If exists is followed by something other than the identifier for a conditional variable, the compiler must issue an error.

\exists\ /ConditionalVariableIdentifier/

The sample doesn't show the rest of the conditionalif statement.