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).
HTML Document Meta. An HTML document head element is used to provide information about a web page to web browsers and search engines, and to link external resources to the page. It does not contain content that is visible on the web page, but that doesnât mean that it is unimportant.