class Nokogiri::XML::NodeSet

def attr key, value = nil, &blk

on all Node objects in the NodeSet.
Set the attribute +key+ to +value+ or the return value of +blk+
## 
def attr key, value = nil, &blk
  unless Hash === key || key && (value || blk)
    return first.attribute(key)
  end
  hash = key.is_a?(Hash) ? key : { key => value }
  hash.each { |k,v| each { |el| el[k] = v || blk[el] } }
  self
end