Comment 1 for bug 693468

The solution proposed in [2] is complicated by the fact that the subfield separator is configurable, but by checking to see if breaker input has a subfield separator in position 4 we can insert the needed indicator placeholders.

This means that users can do either of the following independently:
  * forget to supply indicators
  * fail to supply a leading subfield delimiter

but not both together -- we can't tell the difference between those states programatically.

Implemented in r19049.