C.2 NULL_FILTER Example: Indexing HTML Documents

If your document set is entirely in HTML, then Oracle recommends that you use NULL_FILTER in your filter preference because it does no filtering.

For example, to index an HTML document set, specify the system-defined preferences for NULL_FILTER and HTML_SECTION_GROUP:

create index myindex on docs(htmlfile) indextype is ctxsys.context 
  parameters('filter ctxsys.null_filter
  section group ctxsys.html_section_group');