TIMEVALID()
 Determines whether a specified time is valid
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 Syntax

     TIMEVALID(<cTime>) --> lValid

 Argument

     <cTime>  Designates a character string that contains the time to
     test.

 Returns

     TIMEVALID() returns .T. when <cTime> is a valid time; or .F. when
     <cTime> is an invalid time.

 Description

     With input that requires time manipulation, writing your own UDF to
     check time inputs was unavoidable up to now.  TIMEVALID() permits
     complete checking of a time designation.  You can use this function
     effectively with a VALID clause within a READ mask.

 Note

     .  Note the format for time designations.  There must always be
        two digits for hours, minutes, seconds, and hundredths; otherwise,
        the time it is regarded as invalid.  Valid examples are "12",
        "12:59", "12:59:59", and "12:59:59:99".  By contrast, invalid
        examples are "24", "12:60", or "12:1", and/or "12:".  If you work
        with time strings that are not completely filled and that you need to
        check with TIMEVALID(), then they must be TRIMmed prior to the use of
        TIMEVALID() (see following Examples).

 Examples

     .  Using the VALID clause with TRIM, all valid times are
        accepted, even if no seconds or minutes are specified:

        cBegin  :=  SPACE(11)
        @ 5, 10 SAY "Please input time for beginning work:";
        GET cBegin VALID TIMEVALID(TRIM(cBegin))
        READ

     .  Using a VALID clause without TRIM, hours and minutes must be
        specified, so that TIMEVALID() can confirm a valid time:

        cBegin  :=  SPACE(5)
        @ 5, 10 SAY "Please input time for beginning work:";
        GET cBegin VALID TIMEVALID(cBegin)
        READ