How I set another syntax inside a tag?

[zullcore]

Hello,

I have difficulty understanding how to define a new sytanx inside a tag.

I would like to modify the syntax HTML (Rails) with file .html.erb and what should I add code to define a javascript syntax inside a tag <% content_for :js do %> and close <% end %> ??

Thank you for your attention.

[zullcore]

I try adding code in Rails (HTML).sublime-syntax but not work for me, someone help me please?
Check last line: https://gist.github.com/adrianoresende/f93ce3bd270a22a5b7e43d9385e0d7ed