How to make the whole form readonly?

Hi All,

I have tried to follow the sample in XForm sandbox to make an xml instance readonly:

<xforms:instance id="main-instance" xxforms:readonly="true">

This method works fine in 3.5

Now I am going to migrate to 3.6 but it seems that the input control are not marked readonly by this way.

How can I achieve it?

Thanks in advance

Queenie