A colon in an `!expr` block throws an error

[thothal]

I raised an issue on SO I came along when trying to use the !expr syntax in my rmarkdown YAML header.

While this compiles w/o any problem:

navbar:
   - title: !expr Sys.Date()
     href: "#"
     align: right

this throws an error:

navbar:
   - title: !expr format(Sys.Date(), "Created on: %Y-%d-%m")
     href: "#"
     align: right

After some trial and error, I figured that the colon followed by a space : is the culprit, and I found a workaround by replacing the colon by its Unicode representation:

navbar:
   - title: !expr format(Sys.Date(), "Created on\U003A %Y-%d-%m")
     href: "#"
     align: right

The least we can do is to highlight this in the documentation.

[spgarbet]

In the core specification of YAML the colon is reserved. There are multiple YAML 1.1-isms that are surprising to users.

https://stackoverflow.com/questions/11301650/how-to-escape-indicator-characters-colon-and-hyphen-in-yaml

If you want to submit a PR with the documentation updates you'd like to see, give it a go. Pushing updates to this packages impacts a lot of people and even minor changes take a lot of effort. Best case for a PR like this is it goes onto the edge/main version in github and gets pushed out the next time a change is needed (usually a year or so).