Yes definitely something we need =)

Ideally I'd even want to do it via question validation.

Create a custom validator: http://www.yiiframework.com/wiki/168/create-your-own-validation-rule/

That way you cannot save wrong EM expressions.

No,

Saving wrong expression can be done. Simple exemple :

• Add a question with condition after the question (Q1 only if Q2 > 2 for exemple)
• Add text with TOKEN:ATTRIBUTE wthout token table
• Surely a lot of other .

Some solution for "syntax error" seems OK, but logic, think it's a bad idea (a false logic at set 21 can be a good logic at step 28)

ANd more : this need a complete EM system rewriting ....