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).
As a SOX document is not defined by a DTD, the native XML 1.0 Doctype declaration is not appropriate for a document instance to declare SOX Schema information (note that this may not continue to be true once the W3C Schema WG defines an official mechanism).