Is XML case sensitive?

Yes, XML tags are case sensitive. The tag <Employee> is different from the tag <employee>.

Opening and closing tags must be written with the same case:

<Message>This is incorrect</message>

<message>This is correct</message>

What are Modal and Modeless forms in Windows Forms Application?

Modal Form:

In a modal form Windows application, the last form opened can only be accessed. i.e. the parent form cannot be accessed as long as the child form is open.

Modeless Form:

In case of Modeless form, Parent window generates a child window (as in Modal forms), but the user can access either of the Parent window or Child Window.