Thanks! I believe I now understand the various Types and their Validation rules.
I have a final clarification about your reply concerning the "concept" behind Fieldsets, Groups and Elements. You said "I guess, think in terms of tables and nested tables. each line is a table row. the sets are a nested table inside the line table, each set is a new table row.
for all three to be on the same physical line, they must be in the same set." In particular, you said that "each set is a new table row". I created a form where I had two sets under the same Line but both Sets appeared on the *same* Line (which is what I'd normally expect since they are under the same "Line" object, but you said otherwise). Was your statement just a typo or do I have some sort of problem? See Attached image.
Also, FYI, I have had "Instant email notification" selected on all of my postings but I'm not getting any emails (other than the very 1st one).