XPath with optional element in hierarchy

Question

I don't see why you can't use this:

//table[@id='foo']/tr|//table[@id='foo']/tbody/tr

If you want one expression without node set union:

//tr[(.|parent::tbody)[1]/parent::table[@id='foo']]

In XPath 2.0, the optional step can be expressed as (tbody|.).

//table[@id="foo"]/(tbody|.)/tr

XPathTester.com demo

The pipe (|) denotes union (of two node-sets), the dot (.) denotes identity step (returning just what the previous step did).

This can be expanded to include more optional elements at once:

//table[@id="foo"]/(thead|tbody|tfoot|.)/tr

Use:

   //table[@id="foo"]/*[self::tbody or self::thead or self::tfoot]/tr
   |
   //table[@id="foo"]/tr

Select any tr element that is a child of any table that has an id attribute "foo" or any tr element that is a child of a tbody that is a child any table.