Inherited properties in TOML

explicit.toml

[thing]
name = "demo"

[thing.version_a]
items = ['base1', 'base2', 'first1', 'first2']

[thing.version_b]
items = ['base1', 'base2', 'second1', 'second2']

implicit.toml

[thing]
name = "demo"
items = ['base1', 'base2']

[thing.version_a]
items = ['first1', 'first2']

[thing.version_b]
items = ['second1', 'second2']

inherit.toml

[thing]
name = "demo"
items = ['base1', 'base2']

[thing.version_a]
items = ['+', 'first1', 'first2']

[thing.version_b]
items = ['+', 'second1', 'second2']

[thing.version_c]
items = ['third1', 'third2']

separate.toml

[thing]
name = "demo"
items = ['base1', 'base2']

[thing.version_a]
sub_items = ['first1', 'first2']

[thing.version_b]
sub_items = ['second1', 'second2']

What about separate extend vs inherit directives?

“Extend” would do the job!