How to import Model from local file?

How imported file has to look like inside to work properly?

(File -> Load model from local file...)

Should it be xml or sql? Or something different?

It should be XML and in the same format as the XML you get when you select:

(Generate -> XML code)

from the menus.

In the XML file elements with the tags and are optional. If not present default values are used instead (like random values for the layout).

There is also an XML Schema (v1.1) describing the XML structure here: