Oddity in searching - word not found in section.

Question

I have a table with a blob column that needs to be searchable. A CONTEXT index seems the best bet.
The contents of this blob column are hierarchical in nature, as exemplified by
<obj_entity>
<app_entity>
<obj_key>
<app_id>
444EAE4FB9F34E4687D0F86D87E16430
</app_id>
</obj_key>
<obj_text>
A fair amount of text going on in here, filtered from source documents.
</obj_text>
</app_entity>
</obj_entity>
Now when I query this table for all records where the blob contains the word 'source', I get back the expected records and counts. That is, select count(*) from tablea where contains(field, 'source') > 0 returns the proper number of records.
However, when I specify that the query only retrieve the records where the word 'source' is in the obj_entity section, it returns 0 records. Ditto for within app_entity or within obj_text. Ditto for within obj_text within app_entity within obj_entity. That is, select count(*) from tablea where contains(field, 'source within obj_text') > 0 returns 0.
I've tried specifying the AUTO_SECTION_GROUP, the HTML_SECTION_GROUP, and with creating groups based on XML_SECTION_GROUP and manually adding field sections and zone sections. In the latter case I tried naming the sections with and without underscores, as the documentation is unclear as to whether sections can be named with underscores.
The database is 9.2.0.1. I've also tried this, with similar results, on a 8.1.7.4 database.
My thought is that the problem really is in how the sections are defined, as the more general query does retrieve all records. The fact that the general query returns rows also indicates to me that the other parameters for the CONTEXT index are correct.
Any suggestions?

Answer 1

Try using braces -
source within {obj_text}
This will mask the underscores.