How could I get the value of lang (where lang=eng in book title), for
the first element?
Use:
/*/book[1]/title/@lang
This means:
Select the lang
attribute of the title element that is a child of the first book
child of the top element of the XML document.
To get just the string value of this attribute use the standard XPath function string()
:
string(/*/book[1]/title/@lang)