The category of an HTML tag indicates where the tag can be used.
These HTML elements can be used only where metadata content is allowed, such as in the content of a head element.
Flow content in HTML is made up of flow elements, phrasing content and text content, possibly interspersed with HTML comments and/or white space.
These HTML elements can be used only in HTML code where flow content is allowed, with some additional restrictions in specific cases. In addition, text and HTML elements categorized as phrasing content can also be used where flow content is expected.
Phrasing content in HTML is made up of text content and phrasing elements, possibly interspersed with HTML comments and/or white space.
These HTML elements are allowed to be used in HTML code where either flow content is expected or phrasing content is expected, with some possible restrictions in specific cases.