HorizontalRule corresponds to <hr> element in the default output
format, HTML. Current HTML standard defines <hr> element as
"paragraph-level thematic break". In typography it is often
represented by extra space or centered asterism ("⁂"), but since
FB2 does not support text centering, empty line (similar to extra space)
is the only solution.
Line breaks, on the other hand, don't generate <empty-line />
anymore. Previously line breaks generated <empty-line /> element
inside paragraph, which is not allowed. So, this commit addresses
issue #2424 ("FB2 produced by pandoc doesn't validate").
FB2 does not have a way to represent line breaks inside paragraphs.
They are replaced with LF character, which is not rendered by
FB2 readers, but at least preserves some information.
Only <p> and <empty-line /> are allowed in titles,
but <p> has the same type as an ordinary paragraphs.
Therefore, there is no need to remove emphasis from titles.
Also, don't intersperse paragraph with empty lines.
There were some artifact code blocks around from before
`reference-doc` functionality was implemented. This led to ignoring
the reference-doc in places. Though I fixed this, I kept the old
hacked-up functions instead of replacing them with
`parseXml` (imported from Writers.OOXML) which does this in a
consistent manner. This commit corrects that oversight.
We now pull the filtered blocks and speaker notes out at the top of
the `blocksToSlide` function, and then make SpeakerNotes into a
parameter of the `blocksToSlide'` subfunction. The output is the same,
but the logic should be easier to follow now.
We used to keep a map of the slideId-to-notes for each slide. Since we
now extract them at the slide level, this is overcomplicated, and we
can just extract them before converting a slide and then clear the
state after.
Previously, we had treated it as a `Maybe`. But there is no difference
between not having speaker notes and having empty speaker notes. So we
make the SpeakerNotes newtype into a monoid, and test for memptiness
instead of testing for Just/Nothing.
Internal change: We were getting bad results with the empty text box
created by the conversion of notes into an empty paragraph. So we now
convert the notes at the `blocksToSlide` stage, by `walkM`ing a
function over the blocks that returns `()`, and then filters the notes
out. This avoids the need to have a return value for speaker notes,
and thus avoids the empty TextBox.
Together with the previous commit (256f14c5a), closes#4477.
