  The adiabatic limit of a recently proposed dynamical extension of Taylor
relaxation, \emph{multi-region relaxed magnetohydrodynamics} (MRxMHD) is
summarized, with special attention to the appropriate definition of relative
magnetic helicity. The formalism is illustrated using a simple two-region,
sheared-magnetic-field model similar to the Hahm--Kulsrud--Taylor (HKT)
rippled-boundary slab model. In MRxMHD a linear Grad--Shafranov equation
applies, even at finite ripple amplitude. The adiabatic switching on of
boundary ripple excites a shielding current sheet opposing reconnection at a
resonant surface. The perturbed magnetic field as a function of ripple
amplitude is calculated by invoking conservation of magnetic helicity in the
two regions separated by the current sheet. At low ripple amplitude "half
islands" appear on each side of the current sheet, locking the rotational
transform at the resonant value. Beyond a critical amplitude these islands
disappear and the rotational transform develops a discontinuity across the
current sheet.
