Add missing validation on slider

panel/tests/widgets/test_slider.py

@@ -453,7 +453,7 @@
 def test_editable_slider(document, comm,
     editableslider, start, end, step, val1, val2, val3, diff1):
 
     slider = editableslider(start=start, end=end, value=val1, name='Slider')
 
     widget = slider.get_root(document, comm=comm)
 
@@ -628,7 +628,7 @@
             value=val_init, name='Slider'
         )
     except Exception:
         assert fail_init
 
     try:
         slider.value = val_update
@@ -774,3 +774,19 @@
     slider = editableslider(fixed_end=fixed_end, end=end, step=step)
     assert slider.start == end - step
     assert slider.end == end
+
+@pytest.mark.parametrize(
+    "slider_class,start,end,value",[
+        (FloatSlider, 0, 10, 11),
+        (IntSlider, 0, 10, 11),
+        (EditableFloatSlider, 0,10,11),
+        (EditableIntSlider, 0, 10, 11),
+    ]
+)
+def test_cannot_set_continous_value_outside_bounds(slider_class, start, end, value):
+    with pytest.raises(ValueError):
+        slider_class(value=value, start=start, end=end)
+
+    slider = slider_class(start=start, end=end)
+    with pytest.raises(ValueError):
+        slider.value=value

panel/widgets/slider.py

@@ -105,6 +105,11 @@ def _update_model(
 
 
 class ContinuousSlider(_SliderBase):
+    """The ContinuousSlider is an abstract base class for a slider widget with value, start, end
+    and step parameters.
+
+    It allows selecting a continuous value within a set of bounds using a slider.
+    """
 
     format = param.ClassSelector(class_=(str, TickFormatter,), doc="""
         A custom format string or Bokeh TickFormatter.""")
@@ -116,8 +121,12 @@ class ContinuousSlider(_SliderBase):
     def __init__(self, **params):
         if 'value' not in params:
             params['value'] = params.get('start', self.start)
+
         super().__init__(**params)
 
+        self._validate_value()
+        self.param.watch(self._validate_value, ['value', 'start', 'end'])
+
     def _get_embed_state(self, root, values=None, max_opts=3):
         ref = root.ref['id']
         w_model, parent = self._models[ref]
@@ -165,6 +174,9 @@ def _get_embed_state(self, root, values=None, max_opts=3):
 
         return (dw, w_model, values, lambda x: x.value, 'value', 'cb_obj.value')
 
+    def _validate_value(self, *args):
+        if self.value and not self.start <= self.value <= self.end:
+            raise ValueError(f'Value {self.value} not in bounds {self.start} to {self.end}.')
 
 class FloatSlider(ContinuousSlider):
     """