Documentation

When a key is defined twice, e.g.

name = First
name = Second

When a section is defined twice, e.g.

[foo]
a = 1

[foo]
b = 2

When a key attempts to extend an invalid table

a = {}
[a.b]

b = {}
b.a = 1

c.x.x = 1
[c.a]

When a section attempts to extend a table within an inline array

a = [{ b = 1 }]
[a.c]

When a key is already defined, but attempting to create an implicit array at the same key, e.g.

list = [1, 2, 3]

[[list]]
a = 1

When a non-table value is already defined in a nested key, e.g.

a.b = 1
a.b.c.d = 2

When a non-table value is already defined in a nested implicit array, e.g.

a.b = 1

[[a.b.c]]
d = 2