Once an element's syntax has been defined, we have to address its attributes. All attribute declarations begin with the keyword ATTLIST followed by the element name, attribute name, attribute type, and default data information, as you can see in the following:
<!ATTLIST element-name attribute-name attribute-type default-data>
The HTML 4.0 <BDO> tag type illustrates a small attribute declaration:
<!ATTLIST BDO lang NAME #IMPLIED dir (ltr|rtl) #REQUIRED >
The XML syntax that defines the <bdo> tag under XHTML is similar but you should notice that more attributes are not available for this tag
<!ATTLIST bdo %coreattrs; %events; lang %LanguageCode; #IMPLIED xml:lang %LanguageCode; #IMPLIED dir (ltr|rtl) #REQUIRED >