id — Returns an entities whose ID attributes are in the given
sequence id (
ids any );
The function gets a list of strings, where every string is a
list of IDs delimited by whitespace characters. For every listed
ID, the function checks if the document that contains the context
entity also contains an entity with such ID; if the entity with the
listed ID exists, it is added into the sequence.
To avoid searches of every ID inside the whole document, the
function uses "ID cache" that is created if "IdCache=ENABLE" DTD
configuration option is specified in the call of function that
parses the XML document. In some cases, it is possible to build
such cache on demand if it is not built by a parser, but it
consumes time and in any case it requires the saved DTD information
from the XML parser, so the parser should be specially configured
Note that any attribute of types ID, IDREF or IDREFS is a good
input string for the function id(). So while XQuery "pointer
operator" is not available in XPath expression, the id() function
is a good replacement for it.
The list of strings that consist of IDs
The function ignores any sort of syntax errors on input.
Example24.592.List errors in
List every person who is not a spouse of his own spouse.
document ("census.xml")//person[@spouse and not (. = id (id (@spouse)/person/@spouse)]