this lets you pass ruby keywords to templates:

    <%= render 'example', class: "cool" %>

    <%= render 'example', "spaces are" => "a-ok" %>

    <%= render 'example', Foo: "bar" %>

Previously you'd see confusing syntax errors like this:

    SyntaxError (.../_example.html.erb:1: syntax error, unexpected '='

Now you can reference invalid identifiers through local_assigns.

If you try to use an invalid keyword (e.g. class) in your template, you
get a syntax error on the line where you use it.