From the HTML DTD:
<!ELEMENT A - - (%inline;)* -(A) -- anchor -->
<!ATTLIST A
%attrs; -- %coreattrs, %i18n, %events --
charset %Charset; #IMPLIED -- char encoding of linked resource --
type %ContentType; #IMPLIED -- advisory content type --
name CDATA #IMPLIED -- named link end --
href %URI; #IMPLIED -- URI for linked resource --
hreflang %LanguageCode; #IMPLIED -- language code --
target %FrameTarget; #IMPLIED -- render in this frame --
rel %LinkTypes; #IMPLIED -- forward link types --
rev %LinkTypes; #IMPLIED -- reverse link types --
accesskey %Character; #IMPLIED -- accessibility key character --
shape %Shape; rect -- for use with client-side image maps --
coords %Coords; #IMPLIED -- for use with client-side image maps --
tabindex NUMBER #IMPLIED -- position in tabbing order --
onfocus %Script; #IMPLIED -- the element got the focus --
onblur %Script; #IMPLIED -- the element lost the focus --
>
Which file defines what these entities are, for example %LinkTypes;
or %Script;
?
In the linked HTML DTD are entity declarations such as
<!ENTITY % LinkTypes "CDATA"
-- space-separated list of link types
-->
<!ENTITY % Script "CDATA" -- script expression -->
Given these declarations, you can see that both %LinkTypes;
and %Script;
expand to CDATA
(character data); the comment provides some additional guidance on their intended form or use.