1. A method for video coding, the method comprising: processing a Supplemental Enhancement Information (SEI) Network Abstraction Layer (NAL) unit, comprising a raw byte sequence payload (RBSP) that comprises at least one bitstream partition nesting SEI message structure containing one or more sei_message( ) syntax structures; and coding, within the at least one bitstream partition nesting SEI message structure or from the at least one bitstream partition nesting SEI message structure, a num_seis_in_bsp_minus1 syntax element, the num_seis_in_bsp_minus1 syntax element plus 1 specifying a number of the one or more sei_message( ) syntax structures contained within the at least one bitstream partition nesting SEI message structure, the num_seis_in_bsp_minus1 syntax element being distinct from the one or more sei_message( ) syntax structures.