The vocabulary modules that define element domains have an additional coding requirement. The entity declaration file must include a parameter entity for each element that the domain extends.
The name of the parameter entity is the abbreviation for the domain, followed by a hyphen ("-"), and the name of the element that is extended.
The value of the parameter entity is a list of the specialized elements that can occur in the same locations as the extended element. Each element must be separated by the vertical line ( | ) symbol.
Because the highlighting domain extends the
<ph> element, the entity declaration file for that domain must
include a parameter entity corresponding to the <ph> element. The
name of the entity uses the short name of the domain (hi-d) followed by the
name of the base element. The value includes each specialization of
<ph> in the domain.
<!ENTITY % hi-d-ph "b | u | i | line-through | overline | tt | sup | sub">