Translations:Expression Manager - presentation/95/en
From LimeSurvey Manual
Every question type now has a Relevance option which controls whether the question is displayed or not. The EM processes each Relevance Equation in the order they appear in the survey. If the expression is true (or missing - to support legacy surveys), the question will be displayed. If it is not relevant, then the question will be hidden, and the value will be NULLed in the database. If there are no relevant questions in a group, the entire group will be skipped.