XSLT 2.0 and XPath 2.0 Programmer's Reference, 4th Edition (369 page)

Boolean Expressions

This section concludes the chapter with a description of the operators
and
and
or
.

There is no
not
operator in XPath, it's provided as a function instead, and is described in Chapter 13, on page 850.

Expression	Syntax
OrExpr	AndExpr ( or AndExpr )*
AndExpr	ComparisonExpr ( and ComparisonExpr )*

The syntax shows that the
and
operator binds more tightly than
or
, so that
A
and
B
or
C
and
D
means
(A
and
B)
or
(C
and
D)
. Personally, I prefer to use parentheses to avoid any doubt.