XPath OR operator for different nodes

We want the "attribute" element of @name 'Author' that is following an "attribute" element of @name 'Title' with a value of 'Book n', without any other "attribute" element of @name 'Title' between them (because if there are, then the author authored some other book).

Said differently, it means we want an author of which the first preceding title (the one it "belongs to") is the one we're looking for:

//attribute[@name='Author']
[preceding-sibling::attribute[@name='Title'][1][contains(.,'Book N')]]

N=C => finds <attribute name="Author"><value>James Berry</value></attribute>

N=B => finds nothing

Using keys and/or grouping functions available in XSLT 2.0 would make this easier (and much faster if the file is big).

(SO code parser seems to think '//' stands for 'comments' but in XPath it's not!!! Sigh.)

Try

//book[title/@lang = 'it']

This reads:

• get all book elements
  • that have at least one title
    • which has an attribute lang
      • with a value of "it"

You may find this helpful — it's an article entitled "XPath in Five Paragraphs" by Ronald Bourret.

But in all honesty, //book[title[@lang='it']] and the above should be equivalent, unless your XPath engine has "issues." So it could be something in the code or sample XML that you're not showing us -- for example, your sample is an XML fragment. Could it be that the root element has a namespace, and you aren't counting for that in your query? And you only told us that it didn't work, but you didn't tell us what results you did get.