protected function checkIfBoolean($fieldName, $canUseFlexforms, $sheet, $explanation)
    {
        $this->checkIfSingleInSetNotEmpty(
            $fieldName,
            $canUseFlexforms,
            $sheet,
            $explanation,
            ['0', '1']
        );
    }
protected function checkIfBoolean($fieldName, $canUseFlexforms, $sheet, $explanation)
    {
        $this->checkIfSingleInSetNotEmpty(
            $fieldName,
            $canUseFlexforms,
            $sheet,
            $explanation,
            ['0', '1']
        );
    }
protected function checkIfBoolean ( $ fieldName , $ canUseFlexforms , $ sheet , $ explanation ) { $ this -> checkIfSingleInSetNotEmpty ( $ fieldName , $ canUseFlexforms , $ sheet , $ explanation , [ '0' , '1' ] ) ; }
Checks whether a configuration value has a boolean value.

@param string $fieldName
TS setup field name to extract, must not be empty
@param bool $canUseFlexforms
whether the value can also be set via flexforms (this will be
mentioned in the error message)
@param string $sheet
flexforms sheet pointer, eg. "sDEF", will be ignored if
$canUseFlexforms is set to FALSE
@param string $explanation
a sentence explaining what that configuration value is needed for,
must not be empty

@return void
Checks whether a configuration value has a boolean value .