How can I get all tr elements without id attribute?
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Than
If you're looking for an element that has class a but doesn't have class b, you can do the following.
//*[contains(@class, 'a') and not(contains(@class, 'b'))]
Or if you want to be sure not to match partial.
//*[contains(concat(' ', normalize-space(@class), ' '), ' some-class ') and
not(contains(concat(' ', normalize-space(@class), ' '), ' another-class '))]