XSLT 2.0 and XPath 2.0 Programmer's Reference, 4th Edition (305 page)

The value of the context item is not changed in the body of a
for
expression (described in Chapter 10). It is therefore wrong to write something like:

Instead, you need to write:

Changes in XPath 2.0

In XPath 1.0, the
.
symbol was an abbreviation for the
Step
self::node()
. This restricted its value to being a reference to a node (never an atomic value), and it also imposed certain other restrictions; for example, it was not possible to apply a predicate to
.
. In XPath 2.0 you can use constructs such as
.[*]
which returns the context item only if it is a node that has a child element.

In XPath 1.0,
.
was never undefined—it always had a value, and the value was always a single node. In XPath 2.0, there are many situations in which it can be undefined; for example, it is undefined on entry to a function body written in XSLT or XQuery.

Usage

The two places where
.
is commonly used are: