Rails sanitize remove default allowed tags

How would I use sanitize, but tell it to disallow some enabled by default tags? The documentation states that I can put this in my application.rb

config.after_initialize do
  ActionView::Base.sanitized_allowed_tags.delete 'div'
end

Can I instead pass this as an argument to sanitize?

Yes you can specify which tags and attributes to allow on a per-call basis. From the fine manual:

Custom Use (only the mentioned tags and attributes are allowed, nothing else)

<%= sanitize @article.body, :tags => %w(table tr td), :attributes => %w(id class style) %>

But the problem with that is that :tags has to include all the tags you want to allow.

The sanitize documentation says to

See ActionView::Base for full docs on the available options.

but the documentation is a lie, ActionView::Base says nothing about the available options.

So, as usual, we have to go digging through the source and hope they don't silently change the interface. Tracing through the code a bit yields this:

def tokenize(text, options)
  options[:parent] = []
  options[:attributes] ||= allowed_attributes
  options[:tags]       ||= allowed_tags
  super
end

def process_node(node, result, options)
  result << case node
    when HTML::Tag
      if node.closing == :close
        options[:parent].shift
      else
        options[:parent].unshift node.name
      end

      process_attributes_for node, options

      options[:tags].include?(node.name) ? node : nil
    else
      bad_tags.include?(options[:parent].first) ? nil : node.to_s.gsub(/</, "&lt;")
  end
end

The default value for options[:tags] in tokenize and the way options[:tags] is used in process_node are of interest and tell us that if options[:tags] has anything then it has to include the entire set of allowed tags and there aren't any other options for controlling the tag set.

Also, if we look at sanitize_helper.rb, we see that sanitized_allowed_tags is just a wrapper for the allowed_tags in the whitelist sanitizer:

def sanitized_allowed_tags
  white_list_sanitizer.allowed_tags
end

You should be able to add your own helper that does something like this (untested off-the-top-of-my-head code):

def sensible_sanitize(html, options)
  if options.include? :not_tags
    options[:tags] = ActionView::Base.sanitized_allowed_tags - options[:not_tags]
  end
  sanitize html, options
end

and then you could

<%= sensible_sanitize @stuff, :not_tags => [ 'div' ] %>

to use the standard default tags except for <div>.