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).
1 The term DOCTYPE tells the browser which type of HTML is used on a webpage. 2  In turn, the browsers use DOCTYPE to determine how to render a page. 3  Failing to use DOCTYPE or using a wrong DOCTYPE may load your page in Quirks Mode. Semantic HTML is a coding style where the tags embody what the text is meant to convey. 2  In Semantic HTML, tags like for bold, and for italic should not be used, reason being they just represent formatting, and provide no indication of meaning or structure.