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).
Course details. XML, or Extensible Markup Language, was designed to make information sharing and data interpretation easier. In this course, developer and author Joe Marini takes you through the basic rules of XML, explains its syntax, and covers more advanced topics such as styling your XML with CSS and XSLT and manipulating XML through the DOM.