Also a logic change: The Number panel does not allow free text
anymore, i. e. if something is entered it _must_ be an expression (at
least for the warning to go away).
An exception are plain numbers, also possible in scientific notation.

I. e.:
2+2 <-- not ok
text <-- not ok
${{2+2}} <-- OK
${env:VAR} <-- OK
123 <-- OK
10e-3 <-- OK
(empty) <-- OK