hpricot：Hpricot::Container::Trav#get_element_by_id

everyday Ruby 
>> require "hpricot"
=> true
>> doc = Hpricot('<p>foo1</p><p>foo2</p>')
=> #<Hpricot::Doc {elem <p> "foo1" </p>} {elem <p> "foo2" </p>}>
>> doc.get_element_by_id('p')
=> nil
>> doc = Hpricot('<a id=0><b><a id=1 /></b><c id=2 /></a>')
=> #<Hpricot::Doc {elem <a id="0"> {elem <b> {emptyelem <a id="1">} </b>} {emptyelem <c id="2">} </a>}>
>> doc.get_element_by_id('0')
=> {elem <a id="0"> {elem <b> {emptyelem <a id="1">} </b>} {emptyelem <c id="2">} </a>}
>> doc.get_element_by_id('1')
=> {emptyelem <a id="1">}
>> doc.get_element_by_id('2')
=> {emptyelem <c id="2">}