The operator field specifies the action to be performed by the
    statement. This field can contain an instruction, an assembler
    directive, or a macro call. If the operator is:

    o  An instruction, MACRO-64 generates the binary code for that
       instruction in the object module.

    o  A directive, MACRO-64 performs certain control actions or
       processing operations during source program assembly.

    o  A macro call, MACRO-64 expands the macro.

    Use either a space or a tab stop to terminate the operator
    field; however, Digital recommends that you use the tab stop
    to terminate the operator field.

    In the following source statement, .BLKL is the operator field:

    EXP:    .BLKL   50           ; Table stores expected values