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).
However, it is important to understand that just declaring an encoding inside a document or on the server won't actually change the bytes; you need to save the text in that encoding to apply it to your content. (The declaration just helps the browser interpret the sequences of bytes in which the text is stored.)