Support for message = NA in a different that Quarto would support (using YAML options)

[cderv]

Since 1.42, if a user wants the logging in console, message = NA or warning = NA needs to be used.

Though Quarto is using YAML format for options

#| message: false

As NA is not something in YAML spec, writing it like this does not work

#| message: NA

It required to use !expr

#| message: !expr NA

which adds a layer of explanation.

It would be greate to have another way that can be used in YAML directly.

Or we could also recognized message = "NA" in Quarto context as a the same as message = NA

[yihui]

Sure, we can support the character string "NA".

[yihui]

Done.