There is now a required "type" attribute for each filter; the hook documentation should reflect this.
Type is one of the following as near as I can tell:
FILTER_TYPE_HTML_RESTRICTOR HTML tag and attribute restricting filters.
FILTER_TYPE_MARKUP_LANGUAGE Non-HTML markup language filters that generate HTML.
FILTER_TYPE_TRANSFORM_IRREVERSIBLE Irreversible transformation filters.
FILTER_TYPE_TRANSFORM_REVERSIBLE Reversible transformation filters.
