Not Operator

Negates a boolean expression. If passed a true value, will return false, and vice versa.

What	Type
Syntax	Not(boolExpression)
boolExpression	bool
Return type	bool

Example: Not(IsEmpty($field)), especially useful for filtering:

<SourceFilters>
  <SourceFilter>Not(IsEmpty($field))</SourceFilter>
</SourceFilters>