ROW or RANGE not optional in range specification

http://www.postgresql.org/docs/devel/static/sql-select.html

Either I'm confused about the syntax description rules or the documentation
for this aspect of window definitions is wrong.

The expression:

[ RANGE | ROWS ] BETWEEN frame_start AND frame_end

means that the specification of range or rows is optional - but that
doesn't appear to be the case...

The documentation should read:

{ RANGE | ROWS } BETWEEN frame_start AND frame_end

Same goes for the bare frame_start specification preceding the between
version.

The bare version looks funny without tag but "ORDER BY idx BETWEEN 5
PRECEDING AND CURRENT ROW" isn't obviously wrong until you get a syntax
error...

David J.