hpricot：Hpricot::Container::Trav#insert_before

>> require "hpricot"
=> true
>> doc = Hpricot('<p>foo1</p><p>foo2</p><p>foo3</p>')
=> #<Hpricot::Doc {elem <p> "foo1" </p>} {elem <p> "foo2" </p>} {elem <p> "foo3" </p>}>
>> doc.insert_before(doc.search('p')[2], doc.at('p'))
=> {elem <p> "foo3" </p>}
>> doc
=> #<Hpricot::Doc {elem <p> "foo3" </p>} {elem <p> "foo1" </p>} {elem <p> "foo2" </p>} {elem <p> "foo3" </p>}>
>> doc.insert_before(doc.search('p')[3], doc.search('p')[3])
=> nil
>> doc.search('p')[3]
=> nil
>> doc.search('p')[2]
=> {elem <p> "foo2" </p>}
>> doc.insert_before(doc.search('p')[2], doc.search('p')[2])
=> {elem <p> "foo2" </p>}
>> doc
=> #<Hpricot::Doc {elem <p> "foo3" </p>} {elem <p> "foo1" </p>} {elem <p> "foo2" </p>} {elem <p> "foo2" </p>} {elem <p> "foo3" </p>}>