Problem to open modal windows for a post and whitelistTag html

Hello , I advance a little on my problem and I think I found the solution, but I can not put in a pratique.
I need help.
All my tests are performed locally on my mac and not on the server.
I think the solution is here:
https://meta.discourse.org/t/whitelisting-some-html-tags/24280

But I don’t understand how.
I have edited the file: "/var/www/discourse/app/assets/javascripts/discourse/lib/markdown.js"
and add this line : Discourse.Markdown.whiteListTag(‘label’, ‘for’, ‘modal-one’);
But for="modal-one" disappears again in tag

I write : <label for="modal-one"><a >News</a></label> in the post
and the inspector gives that : <label><a>News</a></label>

Where I am wrong please ?

Thanks.