The database structures typically contain record numbers of text strings
rather than copies of the strings themselves, as this easily allows resizing
of the strings.
io_read_textiorecord_number
Reads the text from record_number and returns it. Results in a Tcl error
if it fails.
io_write_textiorecord_numbertext
Writes text to the requested record_number. Returns 0 for success, -1
for failure