SQL & PL/SQL

I'm trying to use Forms & webutil to upload a text (XML) file into a CLOB variable on the database.

I use webutil_file_transfer.client_to_DB to transfer the file into a BLOB column on a table, this seems to work OK.

I then retrieve this BLOB from the database and try to make it into a CLOB. There's a procedure called DBMS_LOB.CONVERTTOCLOB that looks like it ought to do the job, but it isn't documented anywhere. It's got a number of cryptic parameters that I can't figure out. Does anyone know how to use it?