In biology, cell theory is a scientific theory which describes the properties of cells. These cells are the basic unit of structure in all organisms and also the basic unit of reproduction.
The doctype declaration should be the very first thing in an HTML document, before the <html> tag. The doctype declaration is not an HTML tag; it is an instruction to the web browser about what version of the markup language the page is written in. The doctype declaration refers to a Document Type Definition (DTD).
Windows Presentation Foundation (WPF) is Microsoft's development tool for Web applications and rich client applications. With WPF, developers can use XAML, the Extensible Application Markup Language, to create custom controls, graphics, 3D images and animations that are not available in traditional HTML implementations. Download this free guide.