Missing doc on expression format for ALTER TABLE

Folks,

I've noticed that this statement is missing something:

(from sql-altertable.sgml):

ALTER COLUMN TYPE

 This form changes the type of a column of a table. Indexes and simple table
constraints involving the column will be automatically converted to use the
new column type by reparsing the originally supplied expression. The optional
USING clause specifies how to compute the new column value from the old; if
omitted, the default conversion is the same as an assignment cast from old
data type to new. A USING clause must be provided if there is no implicit or
assignment cast from old to new type.

... nowhere in this file (or anywhere else that I can tell) is the syntax for
the USING expression defined.

--
--Josh

Josh Berkus
Aglio Database Solutions
San Francisco