How can I append an attribute to an xml data value?

Question

I want to add an attribute that doesn't exist, something like
select appendxml(metadata, '/document/@newid', 2) from mytable where id = 1; <=== NO SUCH FUNCTION.
If the attribute already exists, you can call
select updatexml(metadata, '/document/@oldid', 1) from mytable where id = 1;
I don't want to have to do string manipulation to "splice in" the new attribute, then typecast it back to an xmltype. That's a lot of work, is error prone and has performance implications.
Thanks in advance.

Answer 1

The documentation provides all you need :
http://docs.oracle.com/cd/E11882_01/appdev.112/e23094/xdb04cre.htm#ADXDB4269
SQL> with sample_data as (
  2    select xmltype('<document/>') metadata
  3    from dual
  4  )
  5  select insertchildxml(metadata, '/document', '@newid', '2')
  6  from sample_data
  7  ;
INSERTCHILDXML(METADATA,'/DOCU
<document newid="2"/>