Custom formatting for figure and table captions

[wjakethompson]

This question was originally posted on Stack Overflow and was recommended for a feature request here.

By default, bookdown formats figure and table captions as with a colon (:) between the figure/table number and the caption:

Figure 2.1: Here is a nice figure!

As noted by Yihui on Stack Overflow, this is hardcoded by bookdown in parse_fig_labels().

bookdown/R/html.R

Lines 647 to 672 in 5782b2f

	switch(type, fig = {
	if (length(grep('^<p class="caption', content[i - 0:1])) == 0) {
	# remove these labels, because there must be a caption on this or
	# previous line (possible negative case: the label appears in the alt
	# text of <img>)
	labs[[i]] = character(length(lab))
	next
	}
	labs[[i]] = paste0(label_prefix(type), num, ': ')
	k = max(figs[figs <= i])
	content[k] = paste(c(content[k], sprintf('<span id="%s"></span>', lab)), collapse = '')
	}, tab = {
	if (length(grep('^<caption', content[i - 0:1])) == 0) next
	labs[[i]] = sprintf(
	'<span id="%s">%s</span>', lab, paste0(label_prefix(type), num, ': ')
	)
	}, eq = {
	labs[[i]] = sprintf('\\tag{%s}', num)
	k = max(eqns[eqns <= i])
	content[k] = sub(
	'(<span class="math display")', sprintf('\\1 id="%s"', lab), content[k]
	)
	}, {
	labs[[i]] = paste0(label_prefix(type), num, ' ')
	})
	}

It would be nice to be able to control the separator (e.g., use a . or <br/> if we wanted the figure/table number and caption on separate lines).

Relatedly (but maybe a separate issue), it would also be useful to be able to apply CSS to figure/table numbers and captions separately (e.g., bold figure number and italic caption, as required by APA).

Currently, figure captions are all inside a single paragraph tag (e.g., Figure 2.1 here), so it's not possible to apply styling to the elements separately.

<p class="caption">
  Figure 2.1: Here is a nice figure!
</p>

Tables put the table number inside a <span>, so it's possible to style the two pieces separately with CSS in HTML output.

<caption>
  <span id="tab:nice-tab">Table 2.1: </span>
  Here is a nice table!
</caption>

For both figure and table captions in LaTeX output, the {caption} package can be used to apply styling to the individual pieces, as well as set the separator.

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[cderv]

Thanks for the suggestion.

For later reference, this is related to #855 for more flexibility regarding label and numbering.

[cderv]

For reference, officedown::rdocx_document() offers an argument to change table caption: https://davidgohel.github.io/officedown/articles/captions.html#sequence-options-1

not for the same purpose but worth noting that it exists.

[tjmahr]

One related issue: I use the figure plotting hook to use an html 5 figure/figcaption tags. I can include the figure-id in the hook, but bookdown's figure numbering misses these cases because the regex looks for a paragraph tag. It would be nice to support <figcaption> too.

[cderv]

@tjmahr can you open a specific feature request for this so we can look into into it and track separately ? Thank you !

[yihui]

It would be nice to be able to control the separator (e.g., use a . or <br/> if we wanted the figure/table number and caption on separate lines).

The format is no longer hardcoded and can be customized since bookdown 0.22 (PR #1120). Documentation: https://bookdown.org/yihui/bookdown/internationalization.html Below is an example.

First create _bookdown.yml:

language:
  label:
    fig: !expr function(i) paste0('Figure ', i, '<br/> ')

Then an Rmd file:

---
title: "Test"
output:
  bookdown::html_document2
---

# Section one

```{r, fig.cap='A nice figure.'}
plot(1:10)
```

Relatedly (but maybe a separate issue), it would also be useful to be able to apply CSS to figure/table numbers and captions separately

That should indeed be a separate issue. It should be easy to implement (#1428) but I'm not sure if would break anything.