diff --git a/.github/workflows/deploy.yml b/.github/workflows/deploy.yml
index bb4d4a5..e083089 100644
--- a/.github/workflows/deploy.yml
+++ b/.github/workflows/deploy.yml
@@ -35,12 +35,13 @@ jobs:
       - name: Build Coverage Report
         run: XDEBUG_MODE=coverage ./vendor/bin/phpunit -c ./ --coverage-text --coverage-html ./public/coverage
         ### PHPDoc
-      #- name: Create directory public/docs
-      #  run: mkdir ./public/docs
-      #- name: Install PhpDocumentor
-      #  run: wget https://phpdoc.org/phpDocumentor.phar && chmod +x phpDocumentor.phar
-      #- name: Build Documentation
-      #  run: ./phpDocumentor.phar run -d ./src -t ./public/docs
+      - name: Create directory public/docs
+        run: mkdir ./public/docs
+      - name: Install PhpDocumentor
+        ## Support PHP 7.1
+        run: wget https://github.com/phpDocumentor/phpDocumentor/releases/download/v3.1.0/phpDocumentor.phar && chmod +x phpDocumentor.phar
+      - name: Build Documentation
+        run: ./phpDocumentor.phar run -d ./src -t ./public/docs
 
       ### Deploy
       - name: Deploy
diff --git a/composer.json b/composer.json
index cc67ec6..16fb5ea 100644
--- a/composer.json
+++ b/composer.json
@@ -2,6 +2,7 @@
     "name": "phpoffice/math",
     "description": "Math - Manipulate Math Formula",
     "keywords": ["PHP","mathml", "officemathml"],
+    "homepage": "https://phpoffice.github.io/Math/",
     "type": "library",
     "license": "MIT",
     "autoload": {
diff --git a/src/Math/Element/AbstractElement.php b/src/Math/Element/AbstractElement.php
index 3888de9..1eef2c3 100644
--- a/src/Math/Element/AbstractElement.php
+++ b/src/Math/Element/AbstractElement.php
@@ -6,26 +6,4 @@
 
 abstract class AbstractElement
 {
-    /**
-     * @var Math|AbstractGroupElement|null
-     */
-    protected $parent;
-
-    /**
-     * @param Math|AbstractGroupElement|null $parent
-     */
-    public function setParent($parent): self
-    {
-        $this->parent = $parent;
-
-        return $this;
-    }
-
-    /**
-     * @return Math|AbstractGroupElement|null
-     */
-    public function getParent()
-    {
-        return $this->parent;
-    }
 }
diff --git a/src/Math/Element/AbstractGroupElement.php b/src/Math/Element/AbstractGroupElement.php
index 85d97f3..4bc925c 100644
--- a/src/Math/Element/AbstractGroupElement.php
+++ b/src/Math/Element/AbstractGroupElement.php
@@ -12,7 +12,6 @@ abstract class AbstractGroupElement extends AbstractElement
     public function add(AbstractElement $element): self
     {
         $this->elements[] = $element;
-        $element->setParent($this);
 
         return $this;
     }
@@ -23,8 +22,6 @@ public function remove(AbstractElement $element): self
             return $child != $element;
         });
 
-        $element->setParent(null);
-
         return $this;
     }
 
diff --git a/src/Math/Element/Fraction.php b/src/Math/Element/Fraction.php
index 511ac99..8812998 100644
--- a/src/Math/Element/Fraction.php
+++ b/src/Math/Element/Fraction.php
@@ -14,6 +14,12 @@ class Fraction extends AbstractElement
      */
     protected $numerator;
 
+    public function __construct(AbstractElement $numerator, AbstractElement $denominator)
+    {
+        $this->setNumerator($numerator);
+        $this->setDenominator($denominator);
+    }
+
     public function getDenominator(): AbstractElement
     {
         return $this->denominator;
diff --git a/src/Math/Element/Superscript.php b/src/Math/Element/Superscript.php
index 11f1a93..e3a68cc 100644
--- a/src/Math/Element/Superscript.php
+++ b/src/Math/Element/Superscript.php
@@ -14,6 +14,12 @@ class Superscript extends AbstractElement
      */
     protected $superscript;
 
+    public function __construct(AbstractElement $base, AbstractElement $superscript)
+    {
+        $this->setBase($base);
+        $this->setSuperscript($superscript);
+    }
+
     public function getBase(): AbstractElement
     {
         return $this->base;
diff --git a/src/Math/Math.php b/src/Math/Math.php
index 0eaeb2b..13a0e4c 100644
--- a/src/Math/Math.php
+++ b/src/Math/Math.php
@@ -2,48 +2,8 @@
 
 namespace PhpOffice\Math;
 
-use PhpOffice\Math\Element\AbstractElement;
+use PhpOffice\Math\Element\AbstractGroupElement;
 
-class Math
+class Math extends AbstractGroupElement
 {
-    /**
-     * @var AbstractElement[]
-     */
-    protected $elements = [];
-
-    /**
-     * @param Element\AbstractElement $element
-     *
-     * @return self
-     */
-    public function add(Element\AbstractElement $element): self
-    {
-        $this->elements[] = $element;
-        $element->setParent($this);
-
-        return $this;
-    }
-
-    /**
-     * @param Element\AbstractElement $element
-     *
-     * @return self
-     */
-    public function remove(Element\AbstractElement $element): self
-    {
-        $this->elements = array_filter($this->elements, function ($child) use ($element) {
-            return $child != $element;
-        });
-        $element->setParent(null);
-
-        return $this;
-    }
-
-    /**
-     * @return AbstractElement[]
-     */
-    public function getElements(): array
-    {
-        return $this->elements;
-    }
 }
diff --git a/tests/Math/Element/AbstractGroupElementTest.php b/tests/Math/Element/AbstractGroupElementTest.php
new file mode 100644
index 0000000..20c5cf5
--- /dev/null
+++ b/tests/Math/Element/AbstractGroupElementTest.php
@@ -0,0 +1,61 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\PhpOffice\Math\Element;
+
+use PhpOffice\Math\Element;
+use PhpOffice\Math\Element\AbstractGroupElement;
+use PhpOffice\Math\Math;
+use PhpOffice\Math\Reader\MathML;
+use PHPUnit\Framework\TestCase;
+
+class AbstractGroupElementTest extends TestCase
+{
+    /**
+     * @covers \AbstractGroupElement::__construct
+     * @covers \AbstractGroupElement::getElements
+     */
+    public function testConstruct(): void
+    {
+        $row = new Element\Row();
+
+        $this->assertIsArray($row->getElements());
+        $this->assertCount(0, $row->getElements());
+    }
+
+    /**
+     * @covers \AbstractGroupElement::add
+     * @covers \AbstractGroupElement::getElements
+     */
+    public function testAdd(): void
+    {
+        $identifierA = new Element\Identifier('a');
+        $row = new Element\Row();
+
+        $this->assertCount(0, $row->getElements());
+
+        $this->assertInstanceOf(Element\AbstractGroupElement::class, $row->add($identifierA));
+
+        $this->assertCount(1, $row->getElements());
+        $this->assertEquals([$identifierA], $row->getElements());
+    }
+
+    /**
+     * @covers \AbstractGroupElement::add
+     * @covers \AbstractGroupElement::getElements
+     */
+    public function testRemove(): void
+    {
+        $identifierA = new Element\Identifier('a');
+
+        $row = new Element\Row();
+        $row->add($identifierA);
+
+        $this->assertCount(1, $row->getElements());
+
+        $this->assertInstanceOf(Element\AbstractGroupElement::class, $row->remove($identifierA));
+
+        $this->assertCount(0, $row->getElements());
+    }
+}
\ No newline at end of file
diff --git a/tests/Math/Element/FractionTest.php b/tests/Math/Element/FractionTest.php
new file mode 100644
index 0000000..82ab2e8
--- /dev/null
+++ b/tests/Math/Element/FractionTest.php
@@ -0,0 +1,62 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\PhpOffice\Math\Element;
+
+use PhpOffice\Math\Element;
+use PhpOffice\Math\Element\Fraction;
+use PhpOffice\Math\Math;
+use PhpOffice\Math\Reader\MathML;
+use PHPUnit\Framework\TestCase;
+
+class FractionTest extends TestCase
+{
+    /**
+     * @covers \Fraction::__construct
+     */
+    public function testConstruct(): void
+    {
+        $identifierA = new Element\Identifier('a');
+        $identifierB = new Element\Identifier('b');
+
+        $fraction = new Fraction($identifierA, $identifierB);
+
+        $this->assertEquals($identifierA, $fraction->getNumerator());
+        $this->assertEquals($identifierB, $fraction->getDenominator());
+    }
+
+    /**
+     * @covers \Fraction::getNumerator
+     * @covers \Fraction::setNumerator
+     */
+    public function testBase(): void
+    {
+        $identifierA = new Element\Identifier('a');
+        $identifierB = new Element\Identifier('b');
+        $identifierC = new Element\Identifier('c');
+
+        $fraction = new Fraction($identifierA, $identifierB);
+
+        $this->assertEquals($identifierA, $fraction->getNumerator());
+        $this->assertInstanceOf(Fraction::class, $fraction->setNumerator($identifierC));
+        $this->assertEquals($identifierC, $fraction->getNumerator());
+    }
+
+    /**
+     * @covers \Fraction::getDenominator
+     * @covers \Fraction::setDenominator
+     */
+    public function testFraction(): void
+    {
+        $identifierA = new Element\Identifier('a');
+        $identifierB = new Element\Identifier('b');
+        $identifierC = new Element\Identifier('c');
+
+        $fraction = new Fraction($identifierA, $identifierB);
+
+        $this->assertEquals($identifierB, $fraction->getDenominator());
+        $this->assertInstanceOf(Fraction::class, $fraction->setDenominator($identifierC));
+        $this->assertEquals($identifierC, $fraction->getDenominator());
+    }
+}
\ No newline at end of file
diff --git a/tests/Math/Element/IdentifierTest.php b/tests/Math/Element/IdentifierTest.php
new file mode 100644
index 0000000..86d9568
--- /dev/null
+++ b/tests/Math/Element/IdentifierTest.php
@@ -0,0 +1,23 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\PhpOffice\Math\Element;
+
+use PhpOffice\Math\Element;
+use PhpOffice\Math\Element\Identifier;
+use PHPUnit\Framework\TestCase;
+
+class IdentifierTest extends TestCase
+{
+    /**
+     * @covers \Identifier::__construct
+     * @covers \Identifier::getValue
+     */
+    public function testConstruct(): void
+    {
+        $operator = new Identifier('x');
+
+        $this->assertEquals('x', $operator->getValue());
+    }
+}
\ No newline at end of file
diff --git a/tests/Math/Element/NumericTest.php b/tests/Math/Element/NumericTest.php
new file mode 100644
index 0000000..8f00ab4
--- /dev/null
+++ b/tests/Math/Element/NumericTest.php
@@ -0,0 +1,23 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\PhpOffice\Math\Element;
+
+use PhpOffice\Math\Element;
+use PhpOffice\Math\Element\Numeric;
+use PHPUnit\Framework\TestCase;
+
+class NumericTest extends TestCase
+{
+    /**
+     * @covers \Numeric::__construct
+     * @covers \Numeric::getValue
+     */
+    public function testConstruct(): void
+    {
+        $numeric = new Numeric(2);
+
+        $this->assertEquals(2, $numeric->getValue());
+    }
+}
\ No newline at end of file
diff --git a/tests/Math/Element/OperatorTest.php b/tests/Math/Element/OperatorTest.php
new file mode 100644
index 0000000..b3a6779
--- /dev/null
+++ b/tests/Math/Element/OperatorTest.php
@@ -0,0 +1,23 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\PhpOffice\Math\Element;
+
+use PhpOffice\Math\Element;
+use PhpOffice\Math\Element\Operator;
+use PHPUnit\Framework\TestCase;
+
+class OperatorTest extends TestCase
+{
+    /**
+     * @covers \Operator::__construct
+     * @covers \Operator::getValue
+     */
+    public function testConstruct(): void
+    {
+        $operator = new Operator('+');
+
+        $this->assertEquals('+', $operator->getValue());
+    }
+}
\ No newline at end of file
diff --git a/tests/Math/Element/SemanticsTest.php b/tests/Math/Element/SemanticsTest.php
new file mode 100644
index 0000000..b940da9
--- /dev/null
+++ b/tests/Math/Element/SemanticsTest.php
@@ -0,0 +1,45 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\PhpOffice\Math\Element;
+
+use PhpOffice\Math\Element;
+use PhpOffice\Math\Element\Semantics;
+use PhpOffice\Math\Math;
+use PhpOffice\Math\Reader\MathML;
+use PHPUnit\Framework\TestCase;
+
+class SemanticsTest extends TestCase
+{
+    /**
+     * @covers \Semantics::__construct
+     */
+    public function testConstruct(): void
+    {
+        $semantics = new Semantics();
+
+        $this->assertIsArray($semantics->getAnnotations());
+        $this->assertCount(0, $semantics->getAnnotations());
+    }
+
+    /**
+     * @covers \Superscript::addAnnotation
+     * @covers \Superscript::getAnnotation
+     * @covers \Superscript::getAnnotations
+     */
+    public function testAnnotation(): void
+    {
+        $semantics = new Semantics();
+
+        $this->assertIsArray($semantics->getAnnotations());
+        $this->assertCount(0, $semantics->getAnnotations());
+
+        $this->assertInstanceOf(Semantics::class, $semantics->addAnnotation('encoding', 'content'));
+        $this->assertEquals(['encoding' => 'content'], $semantics->getAnnotations());
+        $this->assertCount(1, $semantics->getAnnotations());
+
+        $this->assertEquals('content', $semantics->getAnnotation('encoding'));
+        $this->assertNull($semantics->getAnnotation('notexisting'));
+    }
+}
\ No newline at end of file
diff --git a/tests/Math/Element/SuperscriptTest.php b/tests/Math/Element/SuperscriptTest.php
new file mode 100644
index 0000000..59660b1
--- /dev/null
+++ b/tests/Math/Element/SuperscriptTest.php
@@ -0,0 +1,59 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\PhpOffice\Math\Element;
+
+use PhpOffice\Math\Element;
+use PhpOffice\Math\Element\Superscript;
+use PhpOffice\Math\Math;
+use PhpOffice\Math\Reader\MathML;
+use PHPUnit\Framework\TestCase;
+
+class SuperscriptTest extends TestCase
+{
+    /**
+     * @covers \Superscript::__construct
+     */
+    public function testConstruct(): void
+    {
+        $superscript = new Superscript(new Element\Identifier('a'), new Element\Identifier('a'));
+
+        $this->assertInstanceOf(Element\Identifier::class, $superscript->getBase());
+        $this->assertInstanceOf(Element\Identifier::class, $superscript->getSuperscript());
+    }
+
+    /**
+     * @covers \Superscript::getBase
+     * @covers \Superscript::setBase
+     */
+    public function testBase(): void
+    {
+        $identifierA = new Element\Identifier('a');
+        $identifierB = new Element\Identifier('b');
+        $identifierC = new Element\Identifier('c');
+
+        $superscript = new Superscript($identifierA, $identifierB);
+
+        $this->assertEquals($identifierA, $superscript->getBase());
+        $this->assertInstanceOf(Superscript::class, $superscript->setBase($identifierC));
+        $this->assertEquals($identifierC, $superscript->getBase());
+    }
+
+    /**
+     * @covers \Superscript::getSuperscript
+     * @covers \Superscript::setSuperscript
+     */
+    public function testSuperscript(): void
+    {
+        $identifierA = new Element\Identifier('a');
+        $identifierB = new Element\Identifier('b');
+        $identifierC = new Element\Identifier('c');
+
+        $superscript = new Superscript($identifierA, $identifierB);
+
+        $this->assertEquals($identifierB, $superscript->getSuperscript());
+        $this->assertInstanceOf(Superscript::class, $superscript->setSuperscript($identifierC));
+        $this->assertEquals($identifierC, $superscript->getSuperscript());
+    }
+}
\ No newline at end of file