KEP001: Instantiate things other than widgets from kv

KEP (kv enhancement proposal) 001 instantiate other things than widgets from kv

here we want to be able to create a instance variable as property type e.g. a BoundedNumericProperty using an explicit property type and parameters for that property.

<SomeWidgetClass@Widget>:
    BoundedNumericProperty:
        # currently name seem to be a better idea than id
        # pro id: consistency is good
        # pro name: properties are different from widgets, consistency would be confusing
        name: my_bounded_numeric_property
        min: 20
        max: 50
    
    # alternative proposed syntax 1
    propname(type=BoundedNumericProperty, min=20, max=50): 55

    # alternative proposed syntax 2
    propname:: BoundedNumericProperty
        min: 20
        max: 50
        value: 25
        
    # alternative proposed syntax 3
    propname:: 
        type: BoundedNumericProperty
        min: 20
        max: 50
        value: int(self.text)
        
    # alternative proposed syntax 4
    propname:
        value: 25
        type: BoundedNumericProperty
        min: 20
        max: 50
        
    #5
    propname@BoundedNumericProperty:
        value: int(self.text)  # does this bind to text or not?
        min: 20
        max: 50
    propname: int(self.text)  # bound
    
    #6:
    propname@BoundedNumericProperty:
        value=25
        min=20
        max=50
    propname: int(self.text)
    
    #7
    # issues with this;
    # propname: Widget.center (reusing other property obj) should be illegal
    # doing e.g. propname: BoundedNumericProperty(self.val1, min=self.val2, max=50)
    # won't bind to self.val1/val2 but will only ba evaluated during creation
    propname: BoundedNumericProperty(20, min=20, max=50)
        
    # only syntex 7 seems to allow creation of ReferenceListProperty with many value params
        
        
        
        
    
        
    BoundedNumericProperty:
        # open question, should this trigger an error?, probably not because in py you can do that without error
        name: my_bounded_numeric_property
        min: 20
        max: 50
    
    AliasProperty:
        name: some_alias
        get: app.get_something
        set: app.set_something
        bind: 'something', 'something_else', 'also_something'
        
    Scale:
        value: my_bounded_numeric_property
        on_value: my_bounded_numeric_property = self.value
        
        BoundedNumericProperty:
            # open question, scoping, naming issue?
            name: my_bounded_numeric_property
            min: 20
            max: 50
                  
    Animation:
        # extend to other kind of objects?
        # should it be accessible through id? (can be useful on python side)
        name: my_move
        x: 100
        d: 2
        t: 'in_out_quad'
        
    Button:
        text: 'hey'
        on_press: my_move.start(self)