Database Software

I have a problem with the use of "contains" option within .rtf document.
I have a table (note_tab) in which i put .rtf text:

note_tab (id integer,note varchar2(250));
with primary key on the column id.
Then I have a context index on the column "note":
CREATE INDEX note_idx ON note_tab(note) indextype IS ctxsys.context parameters ('FILTER CTXSYS.AUTO_FILTER');

I inserted in the table some text with .rtf format.
If I try to search some word with the "contains" option then it works.
But I have a problem: if i search a word that is in the table but having different font types, font dimensions, colors etc... in itself , then the "contains" command doesn't work.

For example if I look for the word "country" and this word is in the .rtf text (that I inserted in the table) but it is written like this "co[i]untry", then the "contains" command doesn't find it.

If I do the same thing with an HTML document (instead of a rtf document) using a context index with the NULL_FILTER option, it works!

So is there some option in the creation of the index to ensure the fact that, in .rtf documents, I can find also words with different fonts,dimensions etc.. within themselves?

Thank you
Massimo