1. A decoder for reconstructing a picture from a datastream into which the picture is coded in units of slices into which the picture is partitioned, wherein the decoder is configured to decode the slices from the datastream in accordance with a slice order, the decoder comprising: an entropy decoder configured to entropy decode, using a processor, the slices based on wavefront parallel processing (WPP) in which a current slice of the picture is entropy decoded according to one of at least two modes indicated by a syntax element portion within the current slice, wherein the entropy decoder is configured to: in accordance with a first of the at least two modes indicated by the syntax element portion, decode data related to the current slice from the datastream using context adaptive entropy decoding to obtain a residual signal, the context adaptive entropy decoding comprising a derivation of contexts across slice boundaries, a continuous update of symbol probabilities of the contexts and an initialization of the symbol probabilities depending on saved states of symbol probabilities of a previously decoded slice, in accordance with a second of the at least two modes indicated by the syntax element portion, decode data related to the current slice from the datastream using context adaptive entropy decoding to obtain a residual signal, the context adaptive entropy decoding comprising restricting the derivation of the contexts so as to not cross the slice boundaries, a continuous update of symbol probabilities of the contexts and an initialization of the symbol probabilities independent on a previously decoded slice, and save symbol probabilities as acquired in context adaptive entropy decoding the previously decoded slice up to a second coding block in a row in accordance with a raster scan order, wherein each slice comprises a start syntax portion indicating a position within the picture at which the entropy decoding of the respective slice begins, the entropy decoder being configured to identify entry points of WPP substreams associated with the slices using the slices' start syntax portions; a predictor configured to generate, using the processor, a prediction signal based on prediction parameters related to the current slice from the datastream; and a reconstruction module configured to reconstruct, using the processor, a portion of the picture related to the current slice based on the residual signal and the prediction signal.