Use double-tilde for strikethrough in Markdown tests

[yihui]

The current dev version of commonmark has disabled single tilde for strikethrough: r-lib/commonmark#33 Using double-tilde will make it consistent with Pandoc's Markdown (where single-tilde is for subscripts).

[cpsievert]

Thanks, do you have a timeline in mind for submitting commonmark to CRAN?

[yihui]

I don't, but Jeroen just made a release earlier this month and I'm currently proposing another feature to commonmark, so the next release may not happen very soon.

This particular issue is not urgent, but it will make it possible for me to get rid of an ugly hack in my package. If you can make a new CRAN release of shiny at some point this year, that should be good enough to me. Thanks!

[yihui]

You don't have to skip tests for lower versions of commonmark, because double-tilde works for lower versions, too. Perhaps I didn't make it clear:

• For commonmark <= 1.9.2, both ~text~ and ~~text~~ generate strikethroughs.
• For commonmark > 1.9.2, only ~~text~~ does.