Xpath to check multiple empty children

Question

With the following xml, I'm trying to return true or false depending on whether all <CrucialNumber> elements are empty or not:

<Invoice>
  <Details>
    <LIN1>
      <Quantity>1</Quantity>
      <Product>Test XML</Product>
      <CrucialNumber/>
    </LIN1>
    <LIN1>
      <Quantity>1</Quantity>
      <Product>Test XML</Product>
      <CrucialNumber/>
    </LIN1>
    <LIN1>
      <Quantity>1</Quantity>
      <Product>Test XML</Product>
      <CrucialNumber>123456</CrucialNumber>
    </LIN1>
  </Details>
</Invoice>

The data-type of the CrucialNumber element is string.

So far, these are the xpath expressions I have tried:

string-length(//CrucialNumber/*) > 0;    

not(//CrucialNumber/*[text()]);

./Details/LIN1[*]/CrucialNumber[1] = "";

Answer 1

not(.//CrucialNumber/node())

should do it, it will be true if and only if either (a) there are no CrucialNumber descendant elements at all, or (b) all the descendant CrucialNumber elements are empty.