The Slop decorator implements method missing such that a methods may be used instead of XPath or CSS. See Nokogiri.Slop

Methods
M
R
Constants
XPATH_PREFIX = "./"
 

The default XPath search context for Slop

Instance Public methods
method_missing(name, *args, &block)

look for node with name. See Nokogiri.Slop

# File lib/nokogiri/decorators/slop.rb, line 12
def method_missing name, *args, &block
  if args.empty?
    list = xpath("#{XPATH_PREFIX}#{name.to_s.sub(/^_/, '')}")
  elsif args.first.is_a? Hash
    hash = args.first
    if hash[:css]
      list = css("#{name}#{hash[:css]}")
    elsif hash[:xpath]
      conds = Array(hash[:xpath]).join(' and ')
      list = xpath("#{XPATH_PREFIX}#{name}[#{conds}]")
    end
  else
    CSS::Parser.without_cache do
      list = xpath(
        *CSS.xpath_for("#{name}#{args.first}", :prefix => XPATH_PREFIX)
      )
    end
  end

  super if list.empty?
  list.length == 1 ? list.first : list
end
respond_to_missing?(name, include_private = false)
# File lib/nokogiri/decorators/slop.rb, line 35
def respond_to_missing? name, include_private = false
  list = xpath("#{XPATH_PREFIX}#{name.to_s.sub(/^_/, '')}")

  !list.empty?
end