Slowly pulsating B stars (SPB) and γ Dor stars pulsate in high-order gravity (g-) modes. The frequencies of g-modes are sensitive to the detailed structure and evolution history of stars having convective cores. Receding convective cores in OB-type stars leave behind a chemically inhomogenous ∇_μ>0 radiative zone. Once a g-mode has radial nodes near the boundaries of these layers, the mode gets trapped and its period deviates from asymptotic period spacing. Careful study of such trapped modes

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... lows constraining the extent of such layers by fitting individual pulsation frequencies. We employ 19 consecuitve dipole g-modes of a very rich Kepler SPB pulsator, KIC 10526294, to demonstrate the power of mode trapping in B-stars in studying the thermal and chemical stratification in the overshooting layer.