Possible bug in `element_markdown()`

[fmmattioni]

I have been trying to place the following label on my axis: [La^-] (mmol·L^-1).

The problem is that it seems the use of [ ] and ( ) is causing a bug.

reprex with bug:

library(ggplot2)
library(ggtext)

ggplot(mtcars, aes(mpg, hp)) +
  geom_point() +
  labs(x = "[La<sup>-</sup>] (mmol·L<sup>-1</sup>)") +
  theme(axis.title.x = element_markdown())
#> Error: gridtext has encountered a tag that isn't supported yet: <a>
#> Only a very limited number of tags are currently supported.

^{Created on 2020-06-06 by the reprex package (v0.3.0)}

When I use ( ) instead of [ ], the bug seems to disappear:

library(ggplot2)
library(ggtext)

ggplot(mtcars, aes(mpg, hp)) +
  geom_point() +
  labs(x = "(La<sup>-</sup>) (mmol·L<sup>-1</sup>)") +
  theme(axis.title.x = element_markdown())

^{Created on 2020-06-06 by the reprex package (v0.3.0)}

Any thoughts on this?

[clauswilke]

This happens because the pattern [...] (...) is interpreted as a link in markdown. One workaround is to use the html entities representing [ and ]:

library(ggplot2)
library(ggtext)

ggplot(mtcars, aes(mpg, hp)) +
  geom_point() +
  labs(x = "&#91;La<sup>-</sup>&#93; (mmol·L<sup>-1</sup>)") +
  theme(axis.title.x = element_markdown())

^{Created on 2020-06-06 by the reprex package (v0.3.0)}

The other is to use a non-breaking space. While element_markdown() doesn't actually handle non-breaking spaces correctly, it's sufficient here to stop the markdown interpreter from inserting a link:

library(ggplot2)
library(ggtext)

ggplot(mtcars, aes(mpg, hp)) +
  geom_point() +
  labs(x = "[La<sup>-</sup>]&nbsp;(mmol·L<sup>-1</sup>)") +
  theme(axis.title.x = element_markdown())

^{Created on 2020-06-06 by the reprex package (v0.3.0)}

[fmmattioni]

Oohh, that is true.. I am so sorry, I have completed overlooked this.. thank you, @clauswilke!