Default syntax in case of conflicting file extensions in the Atom text editor

Question

In the Atom text editor, when two language packages define syntax and snippets for files with the same file extension, what determines the precedence?

For example, both language-ruby and language-ruby-on-rails are available by default, as they are included in the so-called Core Package set, and the two packages share the .rb file extension.

How can I make sure that Atom will by default treat .rb file as, say, source.ruby.rails instead of source.ruby files in my projects?

Answer 1

In your config.cson file you can specify filename regexes and a related grammars, like so:

"*":
  "file-types":
    ".rb?$": "source.ruby.rails"