Indexed[]

NIntegrate[]

NIntegrate[Indexed[t, 1], {Indexed[t, 1], 0, 1}]

"Tag Indexed in Indexed[t,1] is Protected"

NIntegrate[Indexed[x, 1]^2 Indexed[x, 2]^2, x [Element] Rectangle[]]

Indexed[]

NIntegrate[]

Integrate[]

Integrate[Indexed[t, 1], {Indexed[t, 1], 0, 1}].