def content
      # Return the cached content from a previous invocation if any
      return @content if @content_cached
      # get the content with a read-write environment from the superclass
      read_write_content = super
      if read_write_content
        tree, env = read_write_content
        # make the content's environment read-only
        if env && !env.is_a?(ReadOnlyEnvironment)
          env = ReadOnlyEnvironment.new(env, env.options)
        end
        @content_cached = true
        @content = [tree, env]
      else
        @content_cached = true
        @content = nil
      end
    end
def content
      # Return the cached content from a previous invocation if any
      return @content if @content_cached
      # get the content with a read-write environment from the superclass
      read_write_content = super
      if read_write_content
        tree, env = read_write_content
        # make the content's environment read-only
        if env && !env.is_a?(ReadOnlyEnvironment)
          env = ReadOnlyEnvironment.new(env, env.options)
        end
        @content_cached = true
        @content = [tree, env]
      else
        @content_cached = true
        @content = nil
      end
    end
The content passed to this environment. If the content's environment isn't already
 read-only, it's made read-only.

 @see BaseEnvironment#content

 @return {[Array<Sass::Tree::Node>, ReadOnlyEnvironment]?} The content nodes and
   the lexical environment of the content block.
   Returns `nil` when there is no content in this environment.