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. In certain cases, authors may specify the value of an attribute without any quotation marks. We recommend using quotation marks even when it is possible to eliminate them. Attribute names are always case-insensitive.
Attribute values are generally case-insensitive.
The definition of each attribute in the reference manual indicates whether its value is case-insensitive. All the attributes defined by this specification are listed in the attribute index . Character references Character references are numeric or symbolic names for characters that may be included in an HTML document. They are useful for referring to rarely used characters, or those that authoring tools make it difficult or impossible to enter. We discuss HTML character references in detail later in the section on the HTML document character set .