diff --git a/src/PhpSpreadsheet/Calculation/Functions.php b/src/PhpSpreadsheet/Calculation/Functions.php
index 8911a5d4..340f5cd0 100644
--- a/src/PhpSpreadsheet/Calculation/Functions.php
+++ b/src/PhpSpreadsheet/Calculation/Functions.php
@@ -131,23 +131,6 @@ class Functions
         return '#Not Yet Implemented';
     }
 
-    /**
-     * NULL.
-     *
-     * Returns the error value #NULL!
-     *
-     * @Deprecated 1.23.0
-     *
-     * @return string #NULL!
-     *
-     *@see Information\ExcelError::null()
-     * Use the null() method in the Information\Error class instead
-     */
-    public static function null()
-    {
-        return Information\ExcelError::null();
-    }
-
     public static function isMatrixValue($idx)
     {
         return (substr_count($idx, '.') <= 1) || (preg_match('/\.[A-Z]/', $idx) > 0);
@@ -215,6 +198,23 @@ class Functions
         return $operand;
     }
 
+    /**
+     * NULL.
+     *
+     * Returns the error value #NULL!
+     *
+     * @Deprecated 1.23.0
+     *
+     * @return string #NULL!
+     *
+     *@see Information\ExcelError::null()
+     * Use the null() method in the Information\Error class instead
+     */
+    public static function null()
+    {
+        return Information\ExcelError::null();
+    }
+
     /**
      * NaN.
      *
@@ -326,7 +326,7 @@ class Functions
      *
      * @Deprecated 1.23.0
      *
-     * @return int|string
+     * @return array|int|string
      *
      * @see Information\ExcelError::type()
      * Use the type() method in the Information\Error class instead
@@ -668,7 +668,7 @@ class Functions
      * @param mixed $cellReference The cell to check
      * @param ?Cell $cell The current cell (containing this formula)
      *
-     * @return bool|string
+     * @return array|bool|string
      */
     public static function isFormula($cellReference = '', ?Cell $cell = null)
     {
@@ -698,4 +698,13 @@ class Functions
     {
         return Worksheet::pregReplace('/:[\\w\$]+$/', '', $coordinate);
     }
+
+    public static function trimSheetFromCellReference(string $coordinate): string
+    {
+        while (strpos($coordinate, '!') !== false) {
+            $coordinate = substr($coordinate, strpos($coordinate, '!') + 1);
+        }
+
+        return $coordinate;
+    }
 }
diff --git a/src/PhpSpreadsheet/Calculation/Information/ExcelError.php b/src/PhpSpreadsheet/Calculation/Information/ExcelError.php
index df003d26..98242eb6 100644
--- a/src/PhpSpreadsheet/Calculation/Information/ExcelError.php
+++ b/src/PhpSpreadsheet/Calculation/Information/ExcelError.php
@@ -2,10 +2,12 @@
 
 namespace PhpOffice\PhpSpreadsheet\Calculation\Information;
 
-use PhpOffice\PhpSpreadsheet\Calculation\Functions;
+use PhpOffice\PhpSpreadsheet\Calculation\ArrayEnabled;
 
 class ExcelError
 {
+    use ArrayEnabled;
+
     /**
      * List of error codes.
      *
@@ -27,11 +29,13 @@ class ExcelError
      *
      * @param mixed $value Value to check
      *
-     * @return int|string
+     * @return array|int|string
      */
     public static function type($value = '')
     {
-        $value = Functions::flattenSingleValue($value);
+        if (is_array($value)) {
+            return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $value);
+        }
 
         $i = 1;
         foreach (self::$errorCodes as $errorCode) {
diff --git a/src/PhpSpreadsheet/Calculation/Information/Value.php b/src/PhpSpreadsheet/Calculation/Information/Value.php
index 21e05d0b..cdb160d7 100644
--- a/src/PhpSpreadsheet/Calculation/Information/Value.php
+++ b/src/PhpSpreadsheet/Calculation/Information/Value.php
@@ -6,6 +6,7 @@ use PhpOffice\PhpSpreadsheet\Calculation\ArrayEnabled;
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
 use PhpOffice\PhpSpreadsheet\Calculation\Functions;
 use PhpOffice\PhpSpreadsheet\Cell\Cell;
+use PhpOffice\PhpSpreadsheet\Cell\Coordinate;
 
 class Value
 {
@@ -170,26 +171,36 @@ class Value
      * @param mixed $cellReference The cell to check
      * @param ?Cell $cell The current cell (containing this formula)
      *
-     * @return bool|string
+     * @return array|bool|string
      */
     public static function isFormula($cellReference = '', ?Cell $cell = null)
     {
         if ($cell === null) {
             return ExcelError::REF();
         }
-        $cellReference = Functions::expandDefinedName((string) $cellReference, $cell);
-        $cellReference = Functions::trimTrailingRange($cellReference);
 
-        preg_match('/^' . Calculation::CALCULATION_REGEXP_CELLREF . '$/i', $cellReference, $matches);
+        $fullCellReference = Functions::expandDefinedName((string) $cellReference, $cell);
 
-        $cellReference = $matches[6] . $matches[7];
+        if (strpos($cellReference, '!') !== false) {
+            $cellReference = Functions::trimSheetFromCellReference($cellReference);
+            $cellReferences = Coordinate::extractAllCellReferencesInRange($cellReference);
+            if (count($cellReferences) > 1) {
+                return self::evaluateArrayArgumentsSubset([self::class, __FUNCTION__], 1, $cellReferences, $cell);
+            }
+        }
+
+        $fullCellReference = Functions::trimTrailingRange($fullCellReference);
+
+        preg_match('/^' . Calculation::CALCULATION_REGEXP_CELLREF . '$/i', $fullCellReference, $matches);
+
+        $fullCellReference = $matches[6] . $matches[7];
         $worksheetName = str_replace("''", "'", trim($matches[2], "'"));
 
         $worksheet = (!empty($worksheetName))
             ? $cell->getWorksheet()->getParent()->getSheetByName($worksheetName)
             : $cell->getWorksheet();
 
-        return ($worksheet !== null) ? $worksheet->getCell($cellReference)->isFormula() : ExcelError::REF();
+        return ($worksheet !== null) ? $worksheet->getCell($fullCellReference)->isFormula() : ExcelError::REF();
     }
 
     /**
diff --git a/src/PhpSpreadsheet/Cell/Cell.php b/src/PhpSpreadsheet/Cell/Cell.php
index 70df0979..87d13104 100644
--- a/src/PhpSpreadsheet/Cell/Cell.php
+++ b/src/PhpSpreadsheet/Cell/Cell.php
@@ -280,7 +280,7 @@ class Cell
      */
     public function getCalculatedValue($resetLog = true)
     {
-        if ($this->dataType == DataType::TYPE_FORMULA) {
+        if ($this->dataType === DataType::TYPE_FORMULA) {
             try {
                 $index = $this->getWorksheet()->getParent()->getActiveSheetIndex();
                 $selected = $this->getWorksheet()->getSelectedCells();
@@ -379,20 +379,16 @@ class Cell
 
     /**
      * Identify if the cell contains a formula.
-     *
-     * @return bool
      */
-    public function isFormula()
+    public function isFormula(): bool
     {
-        return $this->dataType == DataType::TYPE_FORMULA;
+        return $this->dataType === DataType::TYPE_FORMULA && $this->getStyle()->getQuotePrefix() === false;
     }
 
     /**
      *    Does this cell contain Data validation rules?
-     *
-     * @return bool
      */
-    public function hasDataValidation()
+    public function hasDataValidation(): bool
     {
         if (!isset($this->parent)) {
             throw new Exception('Cannot check for data validation when cell is not bound to a worksheet');
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/Div0Test.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/Div0Test.php
new file mode 100644
index 00000000..8655ff0b
--- /dev/null
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/Div0Test.php
@@ -0,0 +1,15 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
+
+use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
+use PHPUnit\Framework\TestCase;
+
+class Div0Test extends TestCase
+{
+    public function testDIV0(): void
+    {
+        $result = ExcelError::DIV0();
+        self::assertEquals('#DIV/0!', $result);
+    }
+}
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/ErrorTypeTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/ErrorTypeTest.php
new file mode 100644
index 00000000..1f22c474
--- /dev/null
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/ErrorTypeTest.php
@@ -0,0 +1,56 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
+
+use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
+use PhpOffice\PhpSpreadsheet\Calculation\Functions;
+use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
+use PHPUnit\Framework\TestCase;
+
+class ErrorTypeTest extends TestCase
+{
+    public function testErrorTypeNoArgument(): void
+    {
+        $result = Functions::errorType();
+        self::assertSame(ExcelError::NA(), $result);
+    }
+
+    /**
+     * @dataProvider providerErrorType
+     *
+     * @param int|string $expectedResult
+     * @param mixed $value
+     */
+    public function testErrorType($expectedResult, $value): void
+    {
+        $result = Functions::errorType($value);
+        self::assertSame($expectedResult, $result);
+    }
+
+    public function providerErrorType(): array
+    {
+        return require 'tests/data/Calculation/Information/ERROR_TYPE.php';
+    }
+
+    /**
+     * @dataProvider providerErrorTypeArray
+     */
+    public function testErrorTypeArray(array $expectedResult, string $values): void
+    {
+        $calculation = Calculation::getInstance();
+
+        $formula = "=ERROR.TYPE({$values})";
+        $result = $calculation->_calculateFormulaValue($formula);
+        self::assertEquals($expectedResult, $result);
+    }
+
+    public function providerErrorTypeArray(): array
+    {
+        return [
+            'vector' => [
+                [[2, 4, 7, ExcelError::NA(), ExcelError::NA(), ExcelError::NA(), 5]],
+                '{5/0, "#REF!", "#N/A", 1.2, TRUE, "PHP", "#NAME?"}',
+            ],
+        ];
+    }
+}
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsErrorTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsErrorTest.php
index 674062ee..26f5b9c3 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsErrorTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsErrorTest.php
@@ -46,8 +46,8 @@ class IsErrorTest extends TestCase
     {
         return [
             'vector' => [
-                [[true, true, true, false, false, false]],
-                '{5/0, "#REF!", "#N/A", 1.2, TRUE, "PHP"}',
+                [[true, true, true, false, false, false, false]],
+                '{5/0, "#REF!", "#N/A", 1.2, TRUE, "PHP", null}',
             ],
         ];
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/IsFormulaTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsFormulaTest.php
similarity index 79%
rename from tests/PhpSpreadsheetTests/Calculation/IsFormulaTest.php
rename to tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsFormulaTest.php
index 40e0d949..03e9bb70 100644
--- a/tests/PhpSpreadsheetTests/Calculation/IsFormulaTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsFormulaTest.php
@@ -1,7 +1,9 @@
 <?php
 
-namespace PhpOffice\PhpSpreadsheetTests\Calculation;
+namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
 
+use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
+use PhpOffice\PhpSpreadsheet\Cell\DataType;
 use PhpOffice\PhpSpreadsheet\NamedRange as NamedRange;
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
 use PHPUnit\Framework\TestCase;
@@ -87,4 +89,26 @@ class IsFormulaTest extends TestCase
 
         $spreadsheet->disconnectWorksheets();
     }
+
+    public function testIsFormulaArray(): void
+    {
+        $spreadsheet = new Spreadsheet();
+        $sheet = $spreadsheet->getActiveSheet();
+        $sheet->getCell('A1')->setValue('=5/2');
+        $sheet->getCell('A2')->setValueExplicit('=5/2', DataType::TYPE_STRING);
+        $sheet->getCell('A3')->setValue('=5/0');
+        $sheet->getCell('A4')->setValue(2.5);
+        $sheet->getCell('A5')->setValue('=NA()');
+        $sheet->getCell('A6')->setValue(true);
+        $sheet->getCell('A7')->setValue('=5/0');
+        $sheet->getCell('A7')->getStyle()->setQuotePrefix(true);
+
+        $calculation = Calculation::getInstance($spreadsheet);
+
+        $formula = '=ISFORMULA(A1:A7)';
+        $result = $calculation->_calculateFormulaValue($formula, 'C1', $sheet->getCell('C1'));
+        self::assertEquals([true, false, true, false, true, false, false], $result);
+
+        $spreadsheet->disconnectWorksheets();
+    }
 }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NaTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NaTest.php
new file mode 100644
index 00000000..471619f3
--- /dev/null
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NaTest.php
@@ -0,0 +1,15 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
+
+use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
+use PHPUnit\Framework\TestCase;
+
+class NaTest extends TestCase
+{
+    public function testNA(): void
+    {
+        $result = ExcelError::NA();
+        self::assertEquals('#N/A', $result);
+    }
+}
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NameTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NameTest.php
new file mode 100644
index 00000000..107e268c
--- /dev/null
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NameTest.php
@@ -0,0 +1,15 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
+
+use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
+use PHPUnit\Framework\TestCase;
+
+class NameTest extends TestCase
+{
+    public function testNAME(): void
+    {
+        $result = ExcelError::NAME();
+        self::assertEquals('#NAME?', $result);
+    }
+}
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NanTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NanTest.php
new file mode 100644
index 00000000..58f97488
--- /dev/null
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NanTest.php
@@ -0,0 +1,15 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
+
+use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
+use PHPUnit\Framework\TestCase;
+
+class NanTest extends TestCase
+{
+    public function testNAN(): void
+    {
+        $result = ExcelError::NAN();
+        self::assertEquals('#NUM!', $result);
+    }
+}
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NullTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NullTest.php
new file mode 100644
index 00000000..87810749
--- /dev/null
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NullTest.php
@@ -0,0 +1,15 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
+
+use PhpOffice\PhpSpreadsheet\Calculation\Functions;
+use PHPUnit\Framework\TestCase;
+
+class NullTest extends TestCase
+{
+    public function testNULL(): void
+    {
+        $result = Functions::null();
+        self::assertEquals('#NULL!', $result);
+    }
+}
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/RefTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/RefTest.php
new file mode 100644
index 00000000..7a8a33de
--- /dev/null
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/RefTest.php
@@ -0,0 +1,15 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
+
+use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
+use PHPUnit\Framework\TestCase;
+
+class RefTest extends TestCase
+{
+    public function testREF(): void
+    {
+        $result = ExcelError::REF();
+        self::assertEquals('#REF!', $result);
+    }
+}
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/ValueTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/ValueTest.php
new file mode 100644
index 00000000..5ab07bd7
--- /dev/null
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/ValueTest.php
@@ -0,0 +1,15 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
+
+use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
+use PHPUnit\Framework\TestCase;
+
+class ValueTest extends TestCase
+{
+    public function testVALUE(): void
+    {
+        $result = ExcelError::VALUE();
+        self::assertEquals('#VALUE!', $result);
+    }
+}
diff --git a/tests/PhpSpreadsheetTests/Calculation/FunctionsTest.php b/tests/PhpSpreadsheetTests/Calculation/FunctionsTest.php
index 16fe8651..c12bf060 100644
--- a/tests/PhpSpreadsheetTests/Calculation/FunctionsTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/FunctionsTest.php
@@ -74,64 +74,6 @@ class FunctionsTest extends TestCase
         self::assertEquals('#Not Yet Implemented', $result);
     }
 
-    public function testDIV0(): void
-    {
-        $result = ExcelError::DIV0();
-        self::assertEquals('#DIV/0!', $result);
-    }
-
-    public function testNA(): void
-    {
-        $result = ExcelError::NA();
-        self::assertEquals('#N/A', $result);
-    }
-
-    public function testNAN(): void
-    {
-        $result = ExcelError::NAN();
-        self::assertEquals('#NUM!', $result);
-    }
-
-    public function testNAME(): void
-    {
-        $result = ExcelError::NAME();
-        self::assertEquals('#NAME?', $result);
-    }
-
-    public function testREF(): void
-    {
-        $result = ExcelError::REF();
-        self::assertEquals('#REF!', $result);
-    }
-
-    public function testNULL(): void
-    {
-        $result = Functions::null();
-        self::assertEquals('#NULL!', $result);
-    }
-
-    public function testVALUE(): void
-    {
-        $result = ExcelError::VALUE();
-        self::assertEquals('#VALUE!', $result);
-    }
-
-    /**
-     * @dataProvider providerErrorType
-     *
-     * @param mixed $expectedResult
-     */
-    public function testErrorType($expectedResult, ...$args): void
-    {
-        $result = Functions::errorType(...$args);
-        self::assertEqualsWithDelta($expectedResult, $result, 1E-8);
-    }
-
-    public function providerErrorType(): array
-    {
-        return require 'tests/data/Calculation/Functions/ERROR_TYPE.php';
-    }
-
     /**
      * @dataProvider providerIfCondition
      *
diff --git a/tests/data/Calculation/Functions/ERROR_TYPE.php b/tests/data/Calculation/Information/ERROR_TYPE.php
similarity index 95%
rename from tests/data/Calculation/Functions/ERROR_TYPE.php
rename to tests/data/Calculation/Information/ERROR_TYPE.php
index b9acafdc..b08d69a6 100644
--- a/tests/data/Calculation/Functions/ERROR_TYPE.php
+++ b/tests/data/Calculation/Information/ERROR_TYPE.php
@@ -1,9 +1,6 @@
 <?php
 
 return [
-    [
-        '#N/A',
-    ],
     [
         '#N/A',
         null,