5.1.3 Labels
  A label is a 1- to 31-character identifier that you use to iden-
  tify a block of statements. All label names must begin with a
  letter; the remaining characters, if any, can be any combi-
  nation of letters, digits, dollar signs ( $ ), underscores ( _ ), or
  periods ( . ), but the final character cannot be a dollar sign.

  Labels have the following advantages over line numbers:

  .
        Meaningful label names provide documentation.
  .
        You can use labels in programs with or without line
        numbers.

  When you use a label to mark a program location, you must
  end the label with a colon ( : ). The colon is used to show that
  the label name is being defined instead of referenced. When
  you reference the label, do not include the colon. In the fol-
  lowing example, the label names end with colons when they
  mark a location, but the colons are not present when the
  labels are referenced:
  OPTION TYPE = EXPLICIT ! Require declarations
  DECLARE INTEGER A
      .
      .
      .
  Outer_loop:
            IF A <> B
            THEN
  Inner_loop:
            IF B = C
              THEN
                  A = A + 1
                  GOTO Outer_loop
              ELSE
                  B = B + 1
                  GOTO Inner_loop
              END IF
            END IF

  Labels have no effect on the order in which program lines
  are executed; they are used to identify a statement or block of
  statements.