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).
Two Methods:Opening XML Files with a BrowserView and Edit XML Files on WindowsCommunity Q&A. XML stands for extensible markup language. HTML is a version of XML used to generate web pages in browsers. The nice thing about XML is that you can use any tags you want and organize them in any way. Many different document formats are based on XML, such as the DOCX format used by Microsoft Word.