Prompted by several things, I finally broke down and updated a couple of chapters to provide some documentation for the ability to use 'dots' for 'missing occsions'. (Note: you can get the list of the data types in MARK that suport the 'dot' covention by lookng at 'Help | Data types']. I'll let the new bits of text and such speak for themselves.
Specifically, new section 2.3 in Chapter 2, and then various worked examples in Chapter 4 (much-expanded sidebar starting on p. 25).
Text is somewhat in 'draft' state, but the basics are in place.