After validating an Expression, I get the message "However, not all control paths can be validated, so it is still possible that parts of your expression are not valid. - What does it mean by control paths?

The expressions are written in JavaScript, which does not compile. What this means is that it doesn't check the code for validity until it runs. When Studytrax validates the expression, it simply runs it to see if JavaScript indicates that there is an error. However, if you have "if" statements, only the ones where the "if" evaluates to true are executed (and checked). So we give the warning to let them know we couldn't check the whole expression.