This is used by the LESS extension - `require("mode/less/less")`
mode is an alias to the CodeMirror mode directory so extensions are independent of where CodeMirror is located, we could arbitrarily adjust this later by turning mode into a plugin. By allowing extensions to require a mode this way (rather than calling some loadBuiltinMode function as a I did earlier) a language can be fully defined by the time the language extension is done loading, rather than making this asynchronous.

There are other ways to load modes, though. For instance `require("text/../CodeMirror2/mode/...")` could work :)