Attributes |
    attribute_name="attribute value"
    attribute_name='attribute value'
Elements may include attributes. The order of attributes within an element tag is not significant and is not guaranteed to be preserved by an XML parser. Attribute values must appear within either single or double quotations. Attribute values within a document must conform to the rules explained in the Section 21.4 of this chapter.

Note that whitespace may appear around the = character.

The value that appears in the quoted string is tested for validity, depending on the attribute type provided in the ATTLIST declaration for the element type. Attribute values can contain general entity references, but cannot contain references to external parsed entities. See the Section 21.4 of this chapter for more information about attribute-value restrictions.