Translations:ExpressionScript Engine - Quick start guide/9/en
From LimeSurvey Manual
Some surveys use "Goto Logic", such that if you answer Question1 with option C, you are redirected to Question5. This approach is very limited since it is hard to validate it. Moreover, it easily breaks when you have to reorder questions. On the other hand, ES uses Boolean relevance equations to specify all the conditions under which a question might be valid. If the question is relevant, then the question is shown, otherwise, it is not applicable, and the value "NULL" is stored in the database.