Translations:ExpressionScript - Presentation/87/en
From LimeSurvey Manual
The "this" variable is used exclusively within the "Whole question validation equation" and "Subquestion validation equation" options (the later is not possible from GUI). It expands to the variable names of each of the cells within those questions. So, if you want to make sure that each entry is greater than three, you would set the "Subquestion validation equation" to (this > 3).