Experimental Physics and
Industrial Control System

The array filter test (modules/database/test/std/filters/arrTest.cpp)
creates "double" array filters that look like:

  {"arr":{},"arr":{"s":x,"e":y,"i":z}}

Apparently this is interpreted by EPICS base to mean two array filters
in succession, first the left, then the right.

According to the JSON standard this is allowed. But is it a good idea?
Are there practical use cases? (The test where I've seen this doesn't
count IMO).