[]

Nothing to capture: an up-level reference is an error

[&x, y, ...]

Capture as specified: identifiers prefixed by & are captured by reference; other identifiers are captured by copy. An up-level reference to any variable not explicitly listed is an error

[&]

Capture by reference: an up-level reference implicitly captures the variable by reference

[=]

Capture by copy: an up-level reference implicitly captures the variable by copy

[&, x, y, ...]

Capture by reference with exceptions: listed variables are captured by value/copy (no listed variable may be prefixed by &)

[=, &x, &y, ...]

Capture by copy with exceptions: listed variables are captured by reference only (every listed variable must be prefixed by &)