FYI these things are unambiguously described in the official XPath Specification regarding the precedence order of operators when evaluating XPath expressions. Specifically, from lowest-to-highest precedence:
...
|4 |or |left-to-right|
|5 |and |left-to-right|
|6 |eq, ne, lt, le, gt, ge, =, !=, <, <=, >, >=, is, <<, >> |left-to-right|
|7 |to |left-to-right|
|8 |+, - |left-to-right|
|9 |*, div, idiv, mod |left-to-right|
Which is to say, AND’s have a higher precedence and are evaluated before ORs (and relational operators before both).
When in doubt, consult the precedence order, or stick a bracket around it 
