Error when export file to web format

Hello to everyone

I have an issue with exporting a ink story in for web format. When I export a file for web, it doesn't recognize this function (To assign a random element of a list.:

~DAY = DAY (RANDOM (1, 3))

For example:

LIST DAY = monday, tuesday, thursday
->Inicio
=== Inicio
~DAY = DAY (RANDOM (1, 3))
Hoy es {DAY}.
-+[Seguir]->Inicio

It works well in the editor, but appears empty in the web export.

Any idea or solution? Thank you very much.