We discuss HTML character entities in detail later in the section on the HTML document character set. Elements An SGML application defines elements that represent structures or desired behavior. The SGML definition of HTML specifies that some HTML elements are not required to have end tags. The definition of each element in the reference manual indicates whether it requires an end tag. Some HTML elements have no content.
Element names are always case-insensitive.
Elements are not tags. For instance, the HEAD element is always present, even though both start and end HEAD tags may be missing in the markup. Attributes Elements may have associated properties, called attributes , to which authors assign values. They may appear in any order. Single quote marks can be included within the attribute value when the value is delimited by double quote marks, and vice versa.