[Zope] Single html checkbox as list?

[clamor@fafalter.de]

Hi,

since I didn't find anything on that topic, the solution might be
obvious but I ran into the following problem:

I have a html form with several checkboxes. If one checkbox is
selected, the variable containing the result is represented by a
string, if two or more checkboxes are selected the variable is
represented by a list.

Is there a way to force the variable to be a list, even if only one
checkbox is selected?

greetings
clamor