method valid_task {
        shift;
        my $r_task = shift;
        return unless defined $r_task;
        my %h_task = %{$r_task};
        my %h_attrs;

        #--- Schedule tag
        if ( !defined $h_task{'schedule'} ) {
            $self->error_log->push('A "schedule" tag is required');
            return 0;
        }
        %h_attrs = %{ $h_task{'schedule'}[0] };
        my %h_schedule_id;
        foreach (keys %h_attrs) {
            if (/^id$/) {
                #--- Schedule id's must be unique
                if (defined $h_schedule_id{'id'}) {
                    $self->error_log->push('Schedule id "'.$h_schedule_id{'id'}.'" is already defined');
                    return 0;
                }
                $h_schedule_id{'id'}++;
            } elsif (/^time$/) {
                #--- A time attribute can have a list of time specifications
                my $s_time_spec = &Utils::trim( $h_attrs{'time'} );
                if ($s_time_spec eq '') {
                    $self->error_log->push('Time specification empty');
                    return 0;
                }
                my @a_time_list = split /$LIST_SEPARATOR/, $s_time_spec;
                foreach (@a_time_list) {
                    if ( !&Utils::valid_time ($_) ) {
                        print 'Time specification "'.$_.'" invalid';
                        $self->error_log->push('Time specification "'.$_.'" invalid');
                        return 0;
                    }
                }
            } else {
                $self->error_log->push('Tag "'.$_.'" not recognized');
                return 0;
            }
        }

        return 1;
    }