What do <lb/>, <pb/>, <gb/> and <cb/> mean?
Do they indicate a beginning, an end, or a transition from one to another?
The spec says <pb/> and <cb/> mark boundaries from one to another but
<lb/> and <gb/> mark beginnings.
. . . Let me tell you a story.</p>
<p><lb/>And so we begin . . .
say there was a blank line in the source at the opening of that new
paragraph? I'd think so, but the spec says no.
Is the difference between page and column breaks on the one hand, and
line and gathering breaks on the other hand, intentional?