+/**
+* \ingroup GUI
+* Implementation of model widget for choice widget definition (combo box)
+* It can be defined as following:
+* \code
+* <choice id="bool_type"
+* label="Type"
+* tooltip="Type of boolean operation"
+* string_list="Cut Fuse Common"
+* />
+* \endcode
+* Aditionally can be used:
+* A key "widget_type". It can have values "combobox" or "radiobuttons".
+* By default it uses "combobox".
+* A key "buttons_dir" which is applicable only for "radiobuttons" mode.
+* It defines direction of radiobuttons layout. it can be "vertical" or "horizontal"
+* Default value is "vertical"
+*/