What version are you using?

2.2.0

What did you do?

I have the file test.js:

/*global a:false */
a = 5;

I have the configuration .eslintrc.yaml:

root: true
rules:
  no-undef: 2

I linted the file with the command-line argument eslint test.js.

What happened?

It did not report any errors.

What did you expect to happen?

I expect it to warn me that I am assigning to a global variable with the false flag, as described in the documentation.