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

mc:Ignorable="d" sets d: prefix as a mark for attributes used in design. Read more on MSDN: mc:Ignorable Attribute

d:DesignHeight="500" and d:DesignWidth="300" use that d: prefix, what makes them available only during design time - they are ignored after standard program compilation.