Syntax:
[begin_label:] WHILE search_condition DO
    statement_list
END WHILE [end_label]

The statement list within a WHILE statement is repeated as long as the
search_condition is true. statement_list consists of one or more
statements.

A WHILE statement can be labeled. end_label cannot be given unless
begin_label also is present. If both are present, they must be the
same.
