Section 101.5.3 (Command for Declaring New Shapes) of chapter 101 (Nodes and Shapes) of the TikZ & PGF manual for version 3.0.1a describes the placement of a node's label with respect to the node's shape as follows (p. 1035).
For a node part called
\pgfnodepartXYZboxis placed at anchor
I find the expression 'placed' ambiguous. How is the box placed at the anchor? Which point of the box coincides with the anchor, and what is the box's direction?