Adobe PHOTOSHOP 6.0 Manual page 183

A path can be closed, with no beginning or end
(for example, a circle), or open, with distinct
endpoints (for example, a wavy line).
Smooth curves are connected by anchor points
called smooth points. Sharply curved paths are
connected by corner points.
Smooth point, and corner point
When you move a direction line on a smooth
point, the curved segments on both sides of the
point adjust simultaneously. By comparison,
when you move a direction line on a corner point,
only the curve on the same side of the point as the
direction line is adjusted.
Adjusting a smooth point, and a corner point
A path does not have to be all one connected series
of segments. It can contain more than one distinct
and separate path component. Each shape in a
shape layer is a path component, as described by
the layer's clipping path.
Separate path components selected
Selecting paths (Photoshop)
You can select path segments and path compo-
nents by clicking with the path component
selection tool or the direct selection tool.
Selecting a shape or segment displays all of the
anchor points on the selected portion, including
any direction lines and direction points if the
selected segment is curved. Direction points
appear as filled circles, selected anchor points as
filled squares, and unselected anchor points as
hollow squares.
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User Guide