question

The question mark operator is something you can put at the end of a label name when getting a label value with the treenode.labelName syntax so that it doesn't throw an exception if the label doesn't exist. You can view the documentation here: https://docs.flexsim.com/en/21.2/Reference/CodingInFlexSim/FlexScriptAPIReference/Tree/treenode.html#Property-labelProperties

The 2 question marks are here so that it doesn't throw exceptions if all your slots don't have a Type label or if all your items don't have a Type label.

?. is similar, but makes it so that no exception is thrown if the thing before the ?. operator doesn't exist. For example, here the ?. makes it so you don't see an exception even though the treenode doesn't exist.

treenode x;
return x?.color;