sub-macroblock for inter prediction for a picture that has three sample arrays or a block of luma samples resulting from a partitioning of a sub-macroblock for inter prediction for a monochrome picture or a picture that is coded using three separate colour planes. 3.152 switching I slice: See SI slice. 3.153 switching P slice: See SP slice. 3.154 syntax element: An element of data represented in the bitstream. 3.155 syntax structure: Zero or more syntax elements present together in the bitstream in a specified order. 3.156 top field: One of two fields that comprise a frame. Each row of a top field is spatially located immediately above the corresponding row of the bottom field. 3.157 top macroblock (of a macroblock pair): The macroblock within a macroblock pair that contains the samples in the top row of samples for the macroblock pair. For a field macroblock pair, the top macroblock represents the samples from the region of the top field of the frame that lie within the spatial region of the macroblock pair. For a frame macroblock pair, the top macroblock represents the samples of the frame that lie within the top half of the spatial region of the macroblock pair. 3.158 transform coefficient: A scalar quantity, considered to be in a frequency domain, that is associated with a particular one-dimensional or two-dimensional frequency index in an inverse transform part of the decoding process. 3.159 transform coefficient level: An integer quantity representing the value associated with a particular two-dimensional frequency index in the decoding process prior to scaling for computation of a transform coefficient value. 3.160 universal unique identifier (UUID): An identifier that is unique with respect to the space of all universal unique identifiers. 3.161 unspecified: The term unspecified, when used in the clauses specifying some values of a particular syntax element, indicates that the values have no specified meaning in this Recommendation | International Standard and will not have a specified meaning in the futu