"The name of the song is called 'Haddocks' Eyes.'"
"Oh, that's the name of the song, is it?" Alice said,
trying to feel interested.
"No, you don't understand," the Knight said, looking
a little vexed. "That's what the name is called.
The name really is 'The Aged Aged Man.'"
"Then I ought to have said 'That's what the song is
called'?" Alice corrected herself.
"No, you oughtn't: that's quite another thing!
The song is called 'Ways And Means': but that's only
what it's called, you know!"
"Well, what is the song, then?" said Alice, who was
by this time completely bewildered.
"I was coming to that," the Knight said. "The song
really is 'A-sitting On A Gate': and the tune's my
own invention."
--
Lewis Carroll, Through The Looking Glass
We're stumbling over the use-mention distinction.
(1) Generally, the name of a thing is not the thing itself.
Accordingly, a key name is the name of a key, and we can talk of "a key" generically without identifying any particular key by name.
(2) A requirement to substitute "key name" in place of "key" stipulates that in this aspect of DITA nomenclature the name is in fact the thing named, and "key" is just a less explicit and careful way of saying "key name".
For example, in
