Error if problem name is empty

[niemela]

It should be an error if a problem has an empty (i.e. empty string or only non-printable characters) name.

This is much more likely now due to the changes in the problem format from legacy. In the new format you can use \problemname to insert the problem name in the statement, in the old this will set the name to empty string.

[thorehusfeldt]

Very cool suggestion. I would look for at least one [[:print:]] and forbid the full match ^[[:space:]]$:

#name: =~ "[[:print:]]" & !~"^[[:space:]]*$"

// The name of this problem, such as "Hello" or { en: "Hello", da: "Hej" }
name!: #name | {[string]: #name}

(I think #name would make sense in many other places where we have string.)