Defines the way highlighted words are decorated: a highlighted word
is surrounded by an element of the form word, where N
is the rank of the fulltext clause (phrase or alternative of terms),
E is the 'element' field of this hiliter (a QName with default value "span"),
A is the 'attribute' field (a QName with default value "class"), and
pattern is a string prefix to the attribute value (by default empty).