I can't find the official documentation for R Markdown YAML frontmatter, for example for this option:
editor_options:
chunk_output_type: console
I've looked into R Markdown: The Definitive Guide (which, by the way, it's the book linked from the official R Markdown website) but it's not there.
I've looked into R Markdown Cookbook, it's hinted at here but doesn't look like the official reference.
I've looked into R Markdown Reference guide, it's not there.
I've looked into R Markdown Cheatsheet, it's not there.