WPF Custom Controls Construction,Triggers and Events

I want to build a new custom control. I found few tutorials that gave me some clue of how to achieve this. As I understand it, creating a new custom control is always done by extending a current one, and it is even possible to extend a control from the very basic levels of the hierarchy, in example, you can even extend:

• UIElement
• FrameworkElement
• Control
• ContentControl
• HeaderedContentControl
• ItemsControl
• Selector
• RangeBase

As written in the following tutorial: http://wpftutorial.net/HowToCreateACustomControl.html

So, I followed the tutorial and created a new project of type Custom Control Library, got my generic .xaml and my code behind. So far so good.

There are 3 types or categories of events I can distinguish between.

1. Events that are consumable by the window (or container) that will use my control: those are the events I would like to expose to the outside. How to write those?

2. Events that are related to the control itself and not being exposed outside; for example, if the mouse is over my control and I would like to react to that. I can do that in the XAML:

   <ControlTemplate.Triggers>
     <Trigger Property="IsMouseOver" Value="true">  
       <Setter Property="Fill" TargetName="LeftTraingularIndicator">  
         <Setter.Value>  
           <SolidColorBrush Color="Yellow" />  
         </Setter.Value>  
       </Setter>
     </Trigger>
   </ControlTemplate.Triggers>  
   

Assuming of couse I have an element with the fill property in my ControlTemplate which is named x:name="LeftTraingularIndicator"

Questions:

Now I want to react in my XAML to IsMouseDown. How do I do that? There is no "IsMouseDown" Trigger. Furthermore what if I want to rea