XSLT 2.0 and XPath 2.0 Programmer's Reference, 4th Edition (502 page)

Predicates

( [ Expr ] )*

The syntax of
KindTest
is given later on page 697. The constructs
QName
,
NCName
, and
Expr
are all defined in the XPath 2.0 grammar, and are described in Chapter 7.

Effect

To describe the effect of a
PatternStep
we'll look at each of its components separately: first the
Pattern- Axis
, then the two kinds of
NodeTest
, that is,
NameTests
and
KindTests
, and finally the
Predicates
.

The PatternAxis

The
PatternAxis
may take the form
attribute::
(abbreviated
@
) or
child::
(abbreviated to nothing:
) In general, if no
PatternAxis
is specified, the child axis is assumed; the only exception is that when the
NodeTest
is an
AttributeTest
(for example,
attribute(*)
) the attribute axis is assumed.