Hevea spacing of tabbing looks wrong

[gasche]

I recently worked on getting a Hevea output for the Menhir manual -- see the corresponding merge request. There was a bug in the visual output that I had to fix, and I think this is a problem with Hevea: I believe that the spacing of the tabbing environment is wrong, at least for this use-case.

Menhir uses tabbing to show a textual representation of parse trees, see Figure 6 in my HTML rendering. In the PDF, it looks roughly as follows:

expression
IF expression THEN expression
                   IF expression THEN expression . ELSE expression

But the default translation of tabbing by Hevea uses the class cellpadding0 for HTML tables generated by tabbing, which sets padding:0; for the <td> columns, which results in the columns between next to each other with no space in between. The Hevea output looks like this:

expression
IF expression THENexpression
                  IF expression THEN expression . ELSE expression

For the Menhir manual, I implemented a workaround, which is to replace all occurrences of cellpadding0 by cellpadding1 in the generated HTML -- see the corresponding commit. This gives me a rendering closer to what LaTeX generates.

As far as I can tell, cellpadding0 is only used for the tabbing environment (open_tabbing in latexscan.mll). What is a reason for not using cellpadding1 there instead? In my case, using cellpadding0 is a rendering bug, but are there other cases where having any padding gives worse rendering? (Where LaTeX would itself not insert any spacing when using tabbing?)

I uploaded with this report a small ZIP archive
repro-hevea-tabbing.zip which contains a minimal reproduction case. I also uploaded online the following files from this example:

• repro-hevea-tabbing.html, which shows the native Hevea output and an image of the LaTeX translation: you see the rendering bug
• repro-hevea-tabbing-fixed.html, which is the same file after replacing cellpadding0 with cellpadding1: it looks less wrong