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).
Function declarations are probably the most familiar and oldest way of doing things in JavaScript land. This creates a variable A which is accessible in the current scope. Scope is a separate topic, so well do everything in the global scope for all these examples (something you want to avoid usually).