exercise - find invalid D tokens (Impossible ?)

[Basile B. via Digitalmars-d-learn]

Here are the specifications of token strings:

"Token strings open with the characters q{ and close with the 
token }. In between must be valid D tokens. The { and }"

So we can deduce that any invalid D token inside a token string 
will lead to a compilation error. Indeed:

void main()
{
     enum s = q{#}; // malformed special token sequence
}

produces an error.

So are you able to find more invalid token ?