Help's Action placeholders

Where can I find the list of placeholders allowed in Actions? Thanks.

Actions that allow placeholders now have a button on the right [>] that gives a list.

Thanks. That shows the names ... is there a list with descriptions? I see none in Help.

There's no special list for actions, but it is a combination of export and columns placeholders.

Except when it isn't e.g. where the same placeholder does different things in the various contexts.