What does mc:Ignorable=“d” mean in WPF?

Question

What does mc:Ignorable=\"d\" mean in WPF?

And this row:

d:DesignHeight=\"500\" 
d:DesignWidth=\"300\"

Answer 1

This a predefined namespace in WPF to be used in design-time,r but will be ignored when actually compiled and executed. It will display your design-time choices but has no effect on the actual layout.

There is an article on the topic.