PX282 - E5b - red giant branch (RGB)

core contracts from increased mass and the envelope expands, so gravitational potential energy is being dumped into the envelope
the temperatures of the core and the shell are increasing
it is known that:

L = 4 π R^{2} σ T_{e f f}^{4}

$L$ is set by fusion
$R$ is increasing
$T_{e f f}$ is decreasing
the envelope becomes convective with a higher gradient: hot core to colder outer
at the end of the RGB, the core gets hot enough for He fusion
so, there is He-burning core, enveloped by a He-shell, enveloped by a H-burning core, enveloped by a H-shell: an onion!