Namespaces

When looking up a template element for copying, two separate namespaces are considered. All section elements live in their own namespace, whereas all non-section elements have their own shared namespace separate from sections. List items have no namespace (lacking a key they can not be referenced at all) and the same applies for fieldset entries, who do have a key but are intentionally excluded from being able to be copied or referenced as template for copying.

non_section_namespace: value
 
non_section_namespace:
- value
- value 

non_section_namespace:
no_namespace = value
no_namespace = value

# section_namespace

Consequently the following document is valid:

template: value
copy < template

# template
# copy < template

Whereas the ones below each aren't because it's unclear which template to copy:

template: value
template: value


copy < template

# template
# template

# copy < template

And lastly the following document is also invalid because fieldset entries can not be copied:

fieldset:
entry = value

copy < entry