X<> vs. X<< >>

perlpodspec gives "two syntaxes" for formatting codes.  There's X<content> and
X<< content >>.  In the "two or more angle brackets" form, the whitespace
immediately following << and preceding >> are not renderable.  That's fine, but
I'm confused as to why that isn't just the universal case.  Is it just a
backcompat issue that someone might have been relying on B< foo > having spaces
at either end?

I've been pondering how to simplify how some things are explained, and that's
one place where I think the spec itself could be simplified without any real
problems.

Also, because it seems almost absurd for the opposite to be true, I'm currently
assuming that a formatting code may *never* have a blank line in its contents.
That is, this is illegal:

  I love you B<

  very
  
  > much.

I realize these are edge cases.  I'm only asking because I'm interested in
opinions, not because I think it will come up frequently.

-- 
rjbs