XML in a Nutshell, 3rd Edition

Attribute Declarations

In addition to declaring its elements, a valid document must declare all the elements’ attributes. This is done with ATTLIST declarations. A single ATTLIST can declare multiple attributes for a single element type. However, if the same attribute is repeated on multiple elements, then it must be declared separately for each element where it appears. (Later in this chapter you’ll see how to use parameter entity references to make this repetition less burdensome.)

For example, ATTLIST declares the source attribute of the image element:

<!ATTLIST image source CDATA #REQUIRED>

It says that the image element has an attribute named source. The value of the source attribute is character data, and instances of the image element in the document are required to provide a value for the source attribute.

A single ATTLIST declaration can declare multiple attributes for the same element. For example, this ATTLIST declaration not only declares the source attribute of the image element, but also the width, height, and alt attributes:

<!ATTLIST image source CDATA #REQUIRED
                width  CDATA #REQUIRED
                height CDATA #REQUIRED
                alt    CDATA #IMPLIED
>

This declaration says the source, width, and height attributes are required. However, the alt attribute is optional and may be omitted from particular image elements. All four attributes are declared to contain character data, the most generic attribute type.

This declaration has the same effect and meaning as four separate ATTLIST declarations, ...