"The American and the British are two peoples, separated by a common language"....Patton, the movie.
So...way back in the beginning of 7th Edition, when formations and detachments all came out, it was driving the American 40K bloggers crazy.
Imagine if you can for a moment...you are a Brit. You wrote some rules. Nobody seemed to understand what you wrote. You decide that its not worth explaining. Later, you write other books, and try to force or illustrate a correction...
Imagine, all along...that each player was to build their army lists in 40K, with every unit fitting into a detachment. Certain combinations of unit inside the detachment could be combined into formations. I postulated that on this blog a while back. And now in recent codexi (Necrons, Eldar), we see it coming to fruition. Is the 7th Edition rule designer truing to impose what he/she intended all along? Decurion anyone?
So, for example, should I take a Baal Strike Force detachment (all units get +1I on the assault) from the Blood Angels Codex, and then include within it some of the formations that are in White Dwarf (note, some of the BA formations don't get the +1I - they get other benefits...like a Decurion the Formation benefits would be added to what those units get within the Detachment)?
Should I take a Combined Arms Detachment from the BRB, and fit within it the Blood Angels Battle Company Formation from the Codex (similar, except that everything is Obsec)?
Why is the BA Battle Company Formation not a Detachment in its own right?
IIRR, in the text in the BRB, it seems on first reading to imply that formations are a combination of units within a Detachment...but again, I'm an American, trying to interpret what was intended within a rulebook written by a Brit, and then translated to American spelling and such, printed in China, and then shipped here via container ship.
If this was true, imagine that the whole idea of taking multiple CADs was not what was intended (libby tac tac, libby tac tac, libby tac tac, libby tac tac, yada yada). Imagine that a TO implied you could build a tournament list that could have a primary detachment, and then an allied detachment if desired (different from your primary faction). Imagine you could include within those detachments all the formations for that faction you wanted, but a unit could only belong within a single formation.
Translation attempt completed. Sort of.