how do I throw an error of a specific type and reason no javascript block?
You might want to check out the Catch errors library (file 
> Libraries)
That's just how snap shows errors, you can't change it without javascript.
um... the reason feature requests are there is to show features that don't exist. the reason help with snap exists is for help with what does exist. I thought someone already said this, but you can't have special errors, there isn't much of a reason to. so, just use the Feature Requests topic you already have, because this topic is asking how to use a feature that doesn't exist. tell me if I missed anything.
Originally, they were wondering how to do something. Now they know that they can't, and so created a feature request. Finally, they linked to their feature request topic here so people can see what was going on.
oh, it was unclear for me because both were made 23h ago.
Right. No problem! (I actually had to try to remember the order of events from yesterday to figure out whether my first instinct about what happened was correct)