Indexing *.txt and extensionless files?

[rsholmes]

It looks as though the Files plugin does not index *.txt files, or files that have no extension. On the other hand it does seem to index files with unknown extensions; I just created a file named "zom.fnog" and it indexed that, but not "groc.txt" in the same directory. So it appears it actively avoids indexing *.txt and extensionless files specifically. Can this behavior be modified? And are there other file extensions it does not index?