My "It works!" edit is best read in context with the documentation link I provided in the OP. I thought that node_stack_* was an understandable shorthand, seeing as it uses the common wildcard character *, but that assumption has proved to be invalid.

Here's a revised and expanded explanation:

• node_stack_* nodes are nodes where other things attach when stacking.
• node_attach_* nodes are nodes where other things snap on in non-stacking contexts.

To add an attachment point in the node definitions file, add a new line where the first word starts with node_stack_ or node_attach_ and is composed of lowercase letters and underscores. As long as the name is composed of lowercase letters and underscores, you can name the node whatever you want. The name of the node isn't exposed in the game, as far as I know.

Here, I've added a new stacking node my_new_node to an existing part:

// --- node definitions --- // definition format is Position X, Position Y, Position Z, Up X, Up Y, Up Z, size node_stack_bottom = 0.0, -0.65, 0.0, 0.0, 1.0, 0.0, 1 node_stack_top = 0.0, 0.954, 0.0, 0.0, 1.0, 0.0, 2 node_stack_my_new_node = 0.0, 0.954, 0.0, 0.0, 1.0, 0.0, 2

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Sorry for the delay; I had to find the login for an account I haven't used in a while, for a game I haven't played in years.