XSLT 2.0 and XPath 2.0 Programmer's Reference, 4th Edition (370 page)

The fact that an
AndExpr
is defined in terms of a
ComparisonExpr
just means that the family of operators including
=
and
eq
are next in precedence order after
and
. These operators were described earlier in this chapter.

An
or
expression returns true if either of its operands is true, while an
and
expression returns true if both of its operands are true.

The operands of
and
and
or
are converted to
xs:boolean
values by taking their effective boolean value. This applies the same rules as for the conditional (
if
) expression described in Chapter 7, and the
boolean()
function, described in Chapter 13. For example, a string is false if it is zero-length, and a sequence is false if it is empty.