HTML & XHTML: The Complete Reference (Osborne Complete Reference Series)

The previous SGML example declares the lang attribute as having values of type NAME , an alphabetic string. NAME is one of several SGML/XML keywords occurring in HTML and XHTML's declarations of an attribute's type:

• CDATA       Unparsed character data

• ID       A document-wide unique identifier

• IDREF       A reference to a document-wide identifier

• NAME       An alphabetic character string plus a hyphen and a period

• NMTOKEN       An alphanumeric character string plus a hyphen and a period

• NUMBER       A character string containing decimal numbers

Notice in early DTD fragment for <bdo> that the dir attribute does not declare its type using a keyword. Instead, the type is specified using an enumerated list containing two possible values, ltr and rtl . In that example for either SGML or XML, the attribute's default behavior is specified with a keyword. A default value may be specified using a quoted string.

• #REQUIRED       A value must be supplied for the attribute.

• #IMPLIED       The attribute is optional.

• #FIXED       The attribute has a fixed value that is declared in quotes using an additional parameter. Because the attribute/value pair is assumed to be constant, it does not need to be used in the document instance.