RFC 5322 specifies the syntax of the email header. In contrast, JCL explicitly specifies all required datasets and devices. A primary key uniquely specifies a tuple within a table. This tag specifies the material name for the element following it. The query declaratively specifies what is to be retrieved. The unit prefix "kibi" specifies multiplication by 2 (1024). The most significant nibble specifies the operation as follows. The user specifies options by coding a series of assembler macros. The ID-2 format specifies a size of . The wide interfaces are managed through a language that specifies implementations. However, the standard only specifies 8"n"-prefetch DRAM, and does not include the flash memory commands. Also, AES67 specifies Multicast or Unicast but many AES67 devices only support Multicast. Thus the standard now specifies seven sizes, each with more than one variant. In some CPUs, each instruction always specifies the address of next instruction. It also specifies when and where to apply security controls.