HTML Writer: LineBlock should use <br>, not <div> with CSS white-space property

[hftf]

Related:

1. Read and write LineBlock elements #3072 22cb9e3 New LineBreak AST element
   HTML Writer converts LineBreak to <div> with style attribute
2. feature request: html output, div around line block #1623 66b0839
   HTML Writer converts LineBreak to <div> with class instead of style attribute
3. Summary of a discussion about rendering RST line blocks to HTML in the Docutils project

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There are problems with using a div with style to indicate a line block. First, it is presentational, not semantic: HTML's <div> does not have the meaning of preserving line breaks, but HTML already does have a semantic element to indicate line breaks: <br>. When CSS is disabled or broken, the block is rendered incorrectly without any line breaks. It also cannot be round-trip converted back into LineBlock:

echo '[LineBlock [[Str "A"],[Str "B"]]]' | pandoc -f native

<div class="line-block">A
B</div>

echo '[LineBlock [[Str "A"],[Str "B"]]]' | pandoc -f native | pandoc -f html -t native

[Div ("",["line-block"],[])
[Plain [Str "A",SoftBreak,Str "B"]]]

I would like to propose that the HTML Writer be modified like so:

echo '[LineBlock [[Str "A"],[Str "B"]]]' | pandoc -f native

<div class="line-block">A<br />
B</div>

and that the HTML Reader also be modified to recognize such markup as LineBlock.

I could also not find any HTML tests for LineBlock (but there are a few in the unmerged PR #1545).

[jgm]

The change was made in #1623. I guess I don't see any reason to prefer using CSS to just putting br tags in there, as long as we still have a div with the special class. But maybe @uvtc or @mb21 would like to comment?

[mb21]

It seems we have being going back and forth on this one a couple of times (e.g. here)... but in principle, I agree, we could just emit <br>s as well -- as long as we also keep the div with the class so people can apply their custom styling with CSS.

Then again, I don't really see much of an advantage for the change either. The two reasons mentioned above seem fairly theoretical. But yes, we could get rid of a few lines of CSS in the templates.

What does @tarleb think, who introduced the LineBlock element?

[uvtc]

If I understand this correctly, the question is whether to use inline css styling "style="white-space: pre-line"", versus <br/>. Regardless we still have the div class=line-block around them.

Since there is no "line block" element in html, I think it makes sense to produce them with <br/>'s. That's exactly what br's are for. I presume each output format has its own "br" for that purpose as well.

[tarleb]

Cutting out any semantical correctnes arguments in this case, I agree that br elements are easier to work with. I slightly favor HTML elements over line break characters, but don't feel stronly either way.

[mb21]

If I understand this correctly, the question is whether to use inline css styling "style="white-space: pre-line"", versus <br/>.

Almost. It's about whether to use <div class="line-block"> and .line-block { white-space: pre-line; } in the template (current implementation), versus <div class="line-block"> with text and <br/>s inside.

[uvtc]

Thanks for the clarification, @mb21 !

[hftf]

Thanks, John.
Fwiw, I also suggested that the HTML Reader recognize <div class="line-block"> as LineBlock.

[jgm]

+++ hftf [Dec 26 17 17:00 ]:

Thanks, John. Fwiw, I also suggested that the HTML Reader recognize <div class="line-block"> as LineBlock.

Done.