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).
Examine the [Content_Types].xml part: Using Windows Explorer, find the file named [Content_Types].xml. Right-click the file, point to Open With, and then click Internet Explorer. In the root of every Office Open XML Formats document is a [Content_Types].xml part. The purpose of the [Content_Types].xml part is to identify every unique type of part found within the document.