On an Confluence platform, there are several existing spaces.
I've just figured out that 3 of them are set as "space template", because when I click on:
'Create Space' / 'Company Manual' (which is a "Space blueprint") / 'Next'
As a result, I get this drop-down list with 3 items:
3-space-templates.png
=> I can find and edit these 3 spaces. However, how have they been set as "template"? In other words, how can I populate this drop-down list myself?