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, ...
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