diff --git a/.github/workflows/php.yml b/.github/workflows/php.yml
index e3b794fa..5496b394 100644
--- a/.github/workflows/php.yml
+++ b/.github/workflows/php.yml
@@ -41,6 +41,10 @@ jobs:
         if: success() || matrix.allow_failure
         run: phpcs -wps --colors
 
+      - name: PHPStan
+        uses: php-actions/phpstan@v3
+        if: success() || matrix.allow_failure
+
   test:
     name: Unit tests with php ${{ matrix.php }} on ${{ matrix.os }}
     runs-on: ${{ matrix.os }}
diff --git a/phpstan-baseline.neon b/phpstan-baseline.neon
new file mode 100644
index 00000000..85d4cd5d
--- /dev/null
+++ b/phpstan-baseline.neon
@@ -0,0 +1,871 @@
+parameters:
+	ignoreErrors:
+		-
+			message: "#^Method ipl\\\\Html\\\\Attribute\\:\\:__construct\\(\\) has parameter \\$value with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/Attribute.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Attribute\\:\\:addValue\\(\\) has parameter \\$value with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/Attribute.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Attribute\\:\\:create\\(\\) has parameter \\$value with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/Attribute.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Attribute\\:\\:escapeValue\\(\\) has parameter \\$value with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/Attribute.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Attribute\\:\\:escapeValue\\(\\) should return string but returns string\\|null\\.$#"
+			count: 1
+			path: src/Attribute.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Attribute\\:\\:getValue\\(\\) return type has no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/Attribute.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Attribute\\:\\:removeValue\\(\\) has parameter \\$value with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/Attribute.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Attribute\\:\\:setValue\\(\\) has parameter \\$value with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/Attribute.php
+
+		-
+			message: "#^Parameter \\#1 \\$value of static method ipl\\\\Html\\\\Attribute\\:\\:escapeValue\\(\\) expects array\\|string, array\\|bool\\|string\\|null given\\.$#"
+			count: 1
+			path: src/Attribute.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\Attribute\\:\\:\\$value type has no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/Attribute.php
+
+		-
+			message: "#^Class ipl\\\\Html\\\\Attributes implements generic interface ArrayAccess but does not specify its types\\: TKey, TValue$#"
+			count: 1
+			path: src/Attributes.php
+
+		-
+			message: "#^Class ipl\\\\Html\\\\Attributes implements generic interface IteratorAggregate but does not specify its types\\: TKey, TValue$#"
+			count: 1
+			path: src/Attributes.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Attributes\\:\\:__construct\\(\\) has parameter \\$attributes with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/Attributes.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Attributes\\:\\:add\\(\\) has parameter \\$attribute with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/Attributes.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Attributes\\:\\:add\\(\\) has parameter \\$value with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/Attributes.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Attributes\\:\\:create\\(\\) has parameter \\$attributes with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/Attributes.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Attributes\\:\\:getIterator\\(\\) return type with generic class ArrayIterator does not specify its types\\: TKey, TValue$#"
+			count: 1
+			path: src/Attributes.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Attributes\\:\\:remove\\(\\) has parameter \\$value with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/Attributes.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Attributes\\:\\:set\\(\\) has parameter \\$attribute with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/Attributes.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Attributes\\:\\:set\\(\\) has parameter \\$value with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/Attributes.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Attributes\\:\\:wantAttributes\\(\\) has parameter \\$attributes with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/Attributes.php
+
+		-
+			message: "#^Parameter \\#1 \\$value of method ipl\\\\Html\\\\Attribute\\:\\:addValue\\(\\) expects array\\|string, array\\|bool\\|string\\|null given\\.$#"
+			count: 3
+			path: src/Attributes.php
+
+		-
+			message: "#^Parameter \\#2 \\$value of method ipl\\\\Html\\\\Attributes\\:\\:set\\(\\) expects array\\|bool\\|string\\|null, mixed given\\.$#"
+			count: 1
+			path: src/Attributes.php
+
+		-
+			message: "#^Parameter \\#2 \\$value of static method ipl\\\\Html\\\\Attribute\\:\\:create\\(\\) expects array\\|bool\\|string\\|null, bool\\|float\\|int\\|string given\\.$#"
+			count: 1
+			path: src/Attributes.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\BaseHtmlElement\\:\\:addAttributes\\(\\) has parameter \\$attributes with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/BaseHtmlElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\BaseHtmlElement\\:\\:addAttributes\\(\\) has parameter \\$attributes with no value type specified in iterable type array\\|ipl\\\\Html\\\\Attributes\\.$#"
+			count: 1
+			path: src/BaseHtmlElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\BaseHtmlElement\\:\\:getDefaultAttributes\\(\\) return type has no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/BaseHtmlElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\BaseHtmlElement\\:\\:registerAttributeCallbacks\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/BaseHtmlElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\BaseHtmlElement\\:\\:removeAttribute\\(\\) has parameter \\$value with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/BaseHtmlElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\BaseHtmlElement\\:\\:setAttribute\\(\\) has parameter \\$value with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/BaseHtmlElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\BaseHtmlElement\\:\\:setAttributes\\(\\) has parameter \\$attributes with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/BaseHtmlElement.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\BaseHtmlElement\\:\\:\\$defaultAttributes type has no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/BaseHtmlElement.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\BaseHtmlElement\\:\\:\\$voidElements type has no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/BaseHtmlElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Contract\\\\FormElement\\:\\:addAttributes\\(\\) has parameter \\$attributes with no value type specified in iterable type iterable\\.$#"
+			count: 1
+			path: src/Contract/FormElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Contract\\\\FormElement\\:\\:getMessages\\(\\) return type has no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/Contract/FormElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Contract\\\\FormElementDecorator\\:\\:decorate\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/Contract/FormElementDecorator.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Contract\\\\ValueCandidates\\:\\:getValueCandidates\\(\\) return type has no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/Contract/ValueCandidates.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Contract\\\\ValueCandidates\\:\\:setValueCandidates\\(\\) has parameter \\$values with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/Contract/ValueCandidates.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Error\\:\\:getPhpTypeName\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/Error.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Error\\:\\:getPhpTypeName\\(\\) has parameter \\$any with no type specified\\.$#"
+			count: 1
+			path: src/Error.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Error\\:\\:renderErrorMessage\\(\\) has parameter \\$message with no type specified\\.$#"
+			count: 1
+			path: src/Error.php
+
+		-
+			message: "#^PHPDoc tag @param has invalid value \\(string\\)\\: Unexpected token \"\\\\n     \\* \", expected variable at offset 24$#"
+			count: 1
+			path: src/Error.php
+
+		-
+			message: "#^Cannot call method hasBeenPressed\\(\\) on ipl\\\\Html\\\\Contract\\\\FormSubmitElement\\|null\\.$#"
+			count: 1
+			path: src/Form.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Form\\:\\:getValues\\(\\) return type has no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/Form.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Form\\:\\:onElementRegistered\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/Form.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Form\\:\\:onError\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/Form.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Form\\:\\:onSuccess\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/Form.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Form\\:\\:populate\\(\\) has parameter \\$values with no value type specified in iterable type iterable\\.$#"
+			count: 1
+			path: src/Form.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Form\\:\\:registerAttributeCallbacks\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/Form.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Form\\:\\:removeElement\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/Form.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Form\\:\\:setRequest\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/Form.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Form\\:\\:setRequest\\(\\) has parameter \\$request with no type specified\\.$#"
+			count: 1
+			path: src/Form.php
+
+		-
+			message: "#^Parameter \\#1 \\$attributes of method ipl\\\\Html\\\\Contract\\\\FormElement\\:\\:addAttributes\\(\\) expects iterable, mixed given\\.$#"
+			count: 1
+			path: src/Form.php
+
+		-
+			message: "#^Parameter \\#1 \\.\\.\\.\\$arrays of function array_merge_recursive expects array, array\\|object\\|null given\\.$#"
+			count: 1
+			path: src/Form.php
+
+		-
+			message: "#^Parameter \\#3 \\$postfix of method ipl\\\\Html\\\\Form\\:\\:addPluginLoader\\(\\) expects string, string\\|null given\\.$#"
+			count: 2
+			path: src/Form.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\Form\\:\\:\\$defaultElementDecorator \\(ipl\\\\Html\\\\Contract\\\\FormElementDecorator\\|null\\) does not accept ipl\\\\Html\\\\Contract\\\\FormElementDecorator\\|ipl\\\\Html\\\\FormDecorator\\\\DecoratorInterface\\.$#"
+			count: 1
+			path: src/Form.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\Form\\:\\:\\$populatedValues type has no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/Form.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\Form\\:\\:\\$submitButton \\(ipl\\\\Html\\\\Contract\\\\FormSubmitElement\\) does not accept null\\.$#"
+			count: 1
+			path: src/Form.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormDecorator\\\\CallbackDecorator\\:\\:assemble\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/FormDecorator/CallbackDecorator.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormDecorator\\\\CallbackDecorator\\:\\:decorate\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/FormDecorator/CallbackDecorator.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormDecorator\\\\DdDtDecorator\\:\\:assemble\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/FormDecorator/DdDtDecorator.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormDecorator\\\\DdDtDecorator\\:\\:dt\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/FormDecorator/DdDtDecorator.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormDecorator\\\\DdDtDecorator\\:\\:renderDescription\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/FormDecorator/DdDtDecorator.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormDecorator\\\\DdDtDecorator\\:\\:renderErrors\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/FormDecorator/DdDtDecorator.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormDecorator\\\\DdDtDecorator\\:\\:renderLabel\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/FormDecorator/DdDtDecorator.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\FormDecorator\\\\DdDtDecorator\\:\\:\\$dd has no type specified\\.$#"
+			count: 1
+			path: src/FormDecorator/DdDtDecorator.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\FormDecorator\\\\DdDtDecorator\\:\\:\\$dt has no type specified\\.$#"
+			count: 1
+			path: src/FormDecorator/DdDtDecorator.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\FormDecorator\\\\DdDtDecorator\\:\\:\\$ready has no type specified\\.$#"
+			count: 1
+			path: src/FormDecorator/DdDtDecorator.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\HtmlDocument\\:\\:\\$wrapper \\(ipl\\\\Html\\\\Contract\\\\Wrappable\\) does not accept null\\.$#"
+			count: 1
+			path: src/FormDecorator/DdDtDecorator.php
+
+		-
+			message: "#^Binary operation \"\\.\" between 'desc_' and array\\|bool\\|string\\|null results in an error\\.$#"
+			count: 1
+			path: src/FormDecorator/DivDecorator.php
+
+		-
+			message: "#^Call to an undefined method ipl\\\\Html\\\\Contract\\\\FormElement\\:\\:ensureAssembled\\(\\)\\.$#"
+			count: 1
+			path: src/FormDecorator/DivDecorator.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormDecorator\\\\DivDecorator\\:\\:assemble\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/FormDecorator/DivDecorator.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormDecorator\\\\DivDecorator\\:\\:assembleDescription\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/FormDecorator/DivDecorator.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormDecorator\\\\DivDecorator\\:\\:assembleElement\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/FormDecorator/DivDecorator.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormDecorator\\\\DivDecorator\\:\\:assembleErrors\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/FormDecorator/DivDecorator.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormDecorator\\\\DivDecorator\\:\\:assembleLabel\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/FormDecorator/DivDecorator.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormDecorator\\\\DivDecorator\\:\\:decorate\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/FormDecorator/DivDecorator.php
+
+		-
+			message: "#^Cannot access offset 'name' on mixed\\.$#"
+			count: 2
+			path: src/FormElement/BaseFormElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\BaseFormElement\\:\\:addValidators\\(\\) has parameter \\$validators with no value type specified in iterable type iterable\\.$#"
+			count: 1
+			path: src/FormElement/BaseFormElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\BaseFormElement\\:\\:getValueCandidates\\(\\) return type has no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/FormElement/BaseFormElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\BaseFormElement\\:\\:getValueOfNameAttribute\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/FormElement/BaseFormElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\BaseFormElement\\:\\:isValid\\(\\) should return bool but returns bool\\|null\\.$#"
+			count: 1
+			path: src/FormElement/BaseFormElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\BaseFormElement\\:\\:registerAttributeCallbacks\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/FormElement/BaseFormElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\BaseFormElement\\:\\:registerCallbacks\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/FormElement/BaseFormElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\BaseFormElement\\:\\:registerValueCallback\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/FormElement/BaseFormElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\BaseFormElement\\:\\:setValidators\\(\\) has parameter \\$validators with no value type specified in iterable type iterable\\.$#"
+			count: 1
+			path: src/FormElement/BaseFormElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\BaseFormElement\\:\\:setValueCandidates\\(\\) has parameter \\$values with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/FormElement/BaseFormElement.php
+
+		-
+			message: "#^Parameter \\#1 \\$attributes of method ipl\\\\Html\\\\BaseHtmlElement\\:\\:addAttributes\\(\\) expects array\\|ipl\\\\Html\\\\Attributes, mixed given\\.$#"
+			count: 1
+			path: src/FormElement/BaseFormElement.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\FormElement\\\\BaseFormElement\\:\\:\\$valueCandidates type has no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/FormElement/BaseFormElement.php
+
+		-
+			message: "#^Trying to invoke mixed but it's not a callable\\.$#"
+			count: 1
+			path: src/FormElement/BaseFormElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\CheckboxElement\\:\\:registerAttributeCallbacks\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/FormElement/CheckboxElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\FieldsetElement\\:\\:getValue\\(\\) has parameter \\$default with no type specified\\.$#"
+			count: 1
+			path: src/FormElement/FieldsetElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\FieldsetElement\\:\\:getValue\\(\\) has parameter \\$name with no type specified\\.$#"
+			count: 1
+			path: src/FormElement/FieldsetElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\FieldsetElement\\:\\:getValues\\(\\) return type has no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/FormElement/FieldsetElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\FieldsetElement\\:\\:onElementRegistered\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/FormElement/FieldsetElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\FieldsetElement\\:\\:populate\\(\\) has parameter \\$values with no value type specified in iterable type iterable\\.$#"
+			count: 1
+			path: src/FormElement/FieldsetElement.php
+
+		-
+			message: "#^Parameter \\#1 \\$attributes of method ipl\\\\Html\\\\Contract\\\\FormElement\\:\\:addAttributes\\(\\) expects iterable, mixed given\\.$#"
+			count: 1
+			path: src/FormElement/FieldsetElement.php
+
+		-
+			message: "#^Parameter \\#1 \\$values of method ipl\\\\Html\\\\FormElement\\\\FieldsetElement\\:\\:populate\\(\\) expects iterable, mixed given\\.$#"
+			count: 1
+			path: src/FormElement/FieldsetElement.php
+
+		-
+			message: "#^Parameter \\#3 \\$postfix of method ipl\\\\Html\\\\FormElement\\\\FieldsetElement\\:\\:addPluginLoader\\(\\) expects string, string\\|null given\\.$#"
+			count: 2
+			path: src/FormElement/FieldsetElement.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\FormElement\\\\FieldsetElement\\:\\:\\$defaultElementDecorator \\(ipl\\\\Html\\\\Contract\\\\FormElementDecorator\\|null\\) does not accept ipl\\\\Html\\\\Contract\\\\FormElementDecorator\\|ipl\\\\Html\\\\FormDecorator\\\\DecoratorInterface\\.$#"
+			count: 1
+			path: src/FormElement/FieldsetElement.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\FormElement\\\\FieldsetElement\\:\\:\\$populatedValues type has no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/FormElement/FieldsetElement.php
+
+		-
+			message: "#^Cannot access offset 0 on mixed\\.$#"
+			count: 1
+			path: src/FormElement/FileElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\FileElement\\:\\:assemble\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/FormElement/FileElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\FileElement\\:\\:registerAttributeCallbacks\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/FormElement/FileElement.php
+
+		-
+			message: "#^Only iterables can be unpacked, array\\<array\\<Psr\\\\Http\\\\Message\\\\UploadedFileInterface\\>\\|Psr\\\\Http\\\\Message\\\\UploadedFileInterface\\>\\|Psr\\\\Http\\\\Message\\\\UploadedFileInterface given in argument \\#1\\.$#"
+			count: 1
+			path: src/FormElement/FileElement.php
+
+		-
+			message: "#^Parameter \\#1 \\$content of static method ipl\\\\Html\\\\Text\\:\\:create\\(\\) expects string, string\\|null given\\.$#"
+			count: 1
+			path: src/FormElement/FileElement.php
+
+		-
+			message: "#^Parameter \\#1 \\$name of method ipl\\\\Html\\\\FormElement\\\\FileElement\\:\\:getFilePath\\(\\) expects string, string\\|null given\\.$#"
+			count: 1
+			path: src/FormElement/FileElement.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\FormElement\\\\FileElement\\:\\:\\$files \\(array\\<Psr\\\\Http\\\\Message\\\\UploadedFileInterface\\>\\) does not accept array\\<Psr\\\\Http\\\\Message\\\\UploadedFileInterface\\|null\\>\\.$#"
+			count: 1
+			path: src/FormElement/FileElement.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\FormElement\\\\FileElement\\:\\:\\$filesToRemove \\(array\\<string\\>\\) does not accept array\\.$#"
+			count: 1
+			path: src/FormElement/FileElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\InputElement\\:\\:registerAttributeCallbacks\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/FormElement/InputElement.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\FormElement\\\\LocalDateTimeElement\\:\\:\\$defaultAttributes type has no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/FormElement/LocalDateTimeElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\PasswordElement\\:\\:registerAttributeCallbacks\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/FormElement/PasswordElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\RadioElement\\:\\:assemble\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/FormElement/RadioElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\RadioElement\\:\\:registerAttributeCallbacks\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/FormElement/RadioElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\RadioElement\\:\\:setDisabledOptions\\(\\) has parameter \\$disabledOptions with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/FormElement/RadioElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\RadioElement\\:\\:setOptions\\(\\) has parameter \\$options with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/FormElement/RadioElement.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\FormElement\\\\RadioElement\\:\\:\\$disabledOptions type has no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/FormElement/RadioElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\RadioOption\\:\\:getLabelCssClass\\(\\) should return array\\<string\\>\\|string but returns mixed\\.$#"
+			count: 1
+			path: src/FormElement/RadioOption.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\SelectElement\\:\\:assemble\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/FormElement/SelectElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\SelectElement\\:\\:getValue\\(\\) return type has no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/FormElement/SelectElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\SelectElement\\:\\:getValue\\(\\) should return array\\|string\\|null but returns mixed\\.$#"
+			count: 2
+			path: src/FormElement/SelectElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\SelectElement\\:\\:makeOption\\(\\) has parameter \\$label with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/FormElement/SelectElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\SelectElement\\:\\:registerAttributeCallbacks\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/FormElement/SelectElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\SelectElement\\:\\:setDisabledOptions\\(\\) has parameter \\$disabledOptions with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/FormElement/SelectElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\SelectElement\\:\\:setOptions\\(\\) has parameter \\$options with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/FormElement/SelectElement.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\FormElement\\\\SelectElement\\:\\:\\$disabledOptions type has no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/FormElement/SelectElement.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\FormElement\\\\SelectElement\\:\\:\\$value type has no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/FormElement/SelectElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\SelectOption\\:\\:assemble\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/FormElement/SelectOption.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormElement\\\\SubmitButtonElement\\:\\:registerAttributeCallbacks\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/FormElement/SubmitButtonElement.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\FormElement\\\\SubmitButtonElement\\:\\:\\$defaultAttributes type has no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/FormElement/SubmitButtonElement.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\FormElement\\\\SubmitElement\\:\\:\\$buttonLabel has no type specified\\.$#"
+			count: 1
+			path: src/FormElement/SubmitElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\FormattedString\\:\\:__construct\\(\\) has parameter \\$args with no value type specified in iterable type iterable\\.$#"
+			count: 1
+			path: src/FormattedString.php
+
+		-
+			message: "#^Parameter \\#2 \\$values of function vsprintf expects array\\<bool\\|float\\|int\\|string\\|null\\>, array\\<ipl\\\\Html\\\\ValidHtml\\> given\\.$#"
+			count: 1
+			path: src/FormattedString.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\FormattedString\\:\\:\\$args \\(array\\<ipl\\\\Html\\\\ValidHtml\\>\\) does not accept array\\<bool\\|float\\|int\\|ipl\\\\Html\\\\ValidHtml\\|string\\>\\.$#"
+			count: 1
+			path: src/FormattedString.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Html\\:\\:__callStatic\\(\\) has parameter \\$arguments with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/Html.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Html\\:\\:escapeForHtml\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/Html.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Html\\:\\:escapeForHtml\\(\\) has parameter \\$content with no type specified\\.$#"
+			count: 1
+			path: src/Html.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Html\\:\\:renderError\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/Html.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Html\\:\\:renderError\\(\\) has parameter \\$error with no type specified\\.$#"
+			count: 1
+			path: src/Html.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Html\\:\\:wrapEach\\(\\) has parameter \\$list with no value type specified in iterable type iterable\\.$#"
+			count: 1
+			path: src/Html.php
+
+		-
+			message: "#^Parameter \\#1 \\$attributes of static method ipl\\\\Html\\\\Attributes\\:\\:wantAttributes\\(\\) expects array\\|ipl\\\\Html\\\\Attributes\\|null, mixed given\\.$#"
+			count: 1
+			path: src/Html.php
+
+		-
+			message: "#^Parameter \\#1 \\$content of class ipl\\\\Html\\\\Text constructor expects string, mixed given\\.$#"
+			count: 1
+			path: src/Html.php
+
+		-
+			message: "#^Access to an undefined property ipl\\\\Html\\\\Contract\\\\Wrappable\\:\\:\\$renderedBy\\.$#"
+			count: 1
+			path: src/HtmlDocument.php
+
+		-
+			message: "#^Call to an undefined method ipl\\\\Html\\\\Contract\\\\Wrappable\\:\\:contains\\(\\)\\.$#"
+			count: 1
+			path: src/HtmlDocument.php
+
+		-
+			message: "#^Call to an undefined method ipl\\\\Html\\\\Contract\\\\Wrappable\\:\\:renderWrappedDocument\\(\\)\\.$#"
+			count: 1
+			path: src/HtmlDocument.php
+
+		-
+			message: "#^Call to an undefined method ipl\\\\Html\\\\Contract\\\\Wrappable\\:\\:wrappedBy\\(\\)\\.$#"
+			count: 1
+			path: src/HtmlDocument.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\HtmlDocument\\:\\:addIndexedContent\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/HtmlDocument.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\HtmlDocument\\:\\:addObjectPosition\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/HtmlDocument.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\HtmlDocument\\:\\:addObjectPosition\\(\\) has parameter \\$pos with no type specified\\.$#"
+			count: 1
+			path: src/HtmlDocument.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\HtmlDocument\\:\\:assemble\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/HtmlDocument.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\HtmlDocument\\:\\:getContent\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/HtmlDocument.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\HtmlDocument\\:\\:incrementIndexKeys\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/HtmlDocument.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\HtmlDocument\\:\\:reIndexContent\\(\\) has no return type specified\\.$#"
+			count: 1
+			path: src/HtmlDocument.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\HtmlDocument\\:\\:\\$contentIndex type has no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/HtmlDocument.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\HtmlDocument\\:\\:\\$renderedBy \\(ipl\\\\Html\\\\HtmlDocument\\) does not accept ipl\\\\Html\\\\Contract\\\\Wrappable\\.$#"
+			count: 1
+			path: src/HtmlDocument.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\HtmlDocument\\:\\:\\$renderedBy \\(ipl\\\\Html\\\\HtmlDocument\\) does not accept null\\.$#"
+			count: 2
+			path: src/HtmlDocument.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\HtmlDocument\\:\\:\\$renderedBy \\(ipl\\\\Html\\\\HtmlDocument\\) in isset\\(\\) is not nullable\\.$#"
+			count: 2
+			path: src/HtmlDocument.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\HtmlDocument\\:\\:\\$wrapped \\(ipl\\\\Html\\\\Contract\\\\Wrappable\\) does not accept null\\.$#"
+			count: 1
+			path: src/HtmlDocument.php
+
+		-
+			message: "#^Parameter \\#1 \\$attributes of static method ipl\\\\Html\\\\Attributes\\:\\:wantAttributes\\(\\) expects array\\|ipl\\\\Html\\\\Attributes\\|null, mixed given\\.$#"
+			count: 1
+			path: src/HtmlElement.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Table\\:\\:row\\(\\) has parameter \\$row with no type specified\\.$#"
+			count: 1
+			path: src/Table.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Table\\:\\:td\\(\\) has parameter \\$attributes with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/Table.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Table\\:\\:td\\(\\) has parameter \\$content with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/Table.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Table\\:\\:th\\(\\) has parameter \\$attributes with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/Table.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Table\\:\\:th\\(\\) has parameter \\$content with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/Table.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Table\\:\\:tr\\(\\) has parameter \\$attributes with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/Table.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\Table\\:\\:tr\\(\\) has parameter \\$content with no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/Table.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\Table\\:\\:\\$body \\(ipl\\\\Html\\\\HtmlElement\\) does not accept ipl\\\\Html\\\\BaseHtmlElement\\.$#"
+			count: 1
+			path: src/Table.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\Table\\:\\:\\$body \\(ipl\\\\Html\\\\HtmlElement\\) does not accept null\\.$#"
+			count: 1
+			path: src/Table.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\Table\\:\\:\\$caption \\(ipl\\\\Html\\\\HtmlElement\\) does not accept ipl\\\\Html\\\\BaseHtmlElement\\.$#"
+			count: 2
+			path: src/Table.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\Table\\:\\:\\$footer \\(ipl\\\\Html\\\\HtmlElement\\) does not accept ipl\\\\Html\\\\BaseHtmlElement\\.$#"
+			count: 1
+			path: src/Table.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\Table\\:\\:\\$header \\(ipl\\\\Html\\\\HtmlElement\\) does not accept ipl\\\\Html\\\\BaseHtmlElement\\.$#"
+			count: 1
+			path: src/Table.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\Table\\:\\:\\$header \\(ipl\\\\Html\\\\HtmlElement\\) does not accept null\\.$#"
+			count: 1
+			path: src/Table.php
+
+		-
+			message: "#^Method ipl\\\\Html\\\\TemplateString\\:\\:__construct\\(\\) has parameter \\$args with no value type specified in iterable type iterable\\.$#"
+			count: 1
+			path: src/TemplateString.php
+
+		-
+			message: "#^Property ipl\\\\Html\\\\TemplateString\\:\\:\\$templateArgs type has no value type specified in iterable type array\\.$#"
+			count: 1
+			path: src/TemplateString.php
diff --git a/phpstan.neon b/phpstan.neon
new file mode 100644
index 00000000..b0402357
--- /dev/null
+++ b/phpstan.neon
@@ -0,0 +1,24 @@
+includes:
+	- phpstan-baseline.neon
+
+parameters:
+    level: max
+
+    checkFunctionNameCase: true
+    checkInternalClassCaseSensitivity: true
+    treatPhpDocTypesAsCertain: false
+
+    paths:
+        - src
+
+    scanDirectories:
+        - vendor
+
+    ignoreErrors:
+        -
+            messages:
+                - '#Unsafe usage of new static\(\)#'
+                - '#. but return statement is missing#'
+            reportUnmatched: false
+
+        - '#Parameter \#2 \$haystack of function in_array expects array.#' # SelectElement::getValues() returns array attribute `multiple` is set to `true`
diff --git a/src/Error.php b/src/Error.php
index a4ab2531..316d237b 100644
--- a/src/Error.php
+++ b/src/Error.php
@@ -29,9 +29,6 @@ public static function show($error)
         if ($error instanceof Throwable) {
             // PHP 7+
             $msg = static::createMessageForException($error);
-        } elseif ($error instanceof Exception) {
-            // PHP 5.x
-            $msg = static::createMessageForException($error);
         } elseif (is_string($error)) {
             $msg = $error;
         } else {
@@ -40,7 +37,7 @@ public static function show($error)
         }
 
         $result = static::renderErrorMessage($msg);
-        if (static::showTraces()) {
+        if (static::showTraces() && $error instanceof Throwable) {
             $result->addHtml(Html::tag('pre', $error->getTraceAsString()));
         }
 
@@ -84,7 +81,7 @@ public static function getPhpTypeName($any)
      */
     protected static function createMessageForException($exception)
     {
-        $file = preg_split('/[\/\\\]/', $exception->getFile(), -1, PREG_SPLIT_NO_EMPTY);
+        $file = preg_split('/[\/\\\]/', $exception->getFile(), -1, PREG_SPLIT_NO_EMPTY) ?: [];
         $file = array_pop($file);
         return sprintf(
             '%s (%s:%d)',
diff --git a/src/Form.php b/src/Form.php
index dc18a5a6..a7360c7d 100644
--- a/src/Form.php
+++ b/src/Form.php
@@ -355,6 +355,8 @@ public function remove(ValidHtml $elementOrHtml)
         }
 
         $this->removeElement($elementOrHtml);
+
+        return $this;
     }
 
     protected function onError()
diff --git a/src/FormDecorator/DdDtDecorator.php b/src/FormDecorator/DdDtDecorator.php
index 1b58ff80..9cfec205 100644
--- a/src/FormDecorator/DdDtDecorator.php
+++ b/src/FormDecorator/DdDtDecorator.php
@@ -51,7 +51,7 @@ public function getAttributes()
         $attributes = parent::getAttributes();
 
         if ($this->wrappedElement->hasBeenValidated() && ! $this->wrappedElement->isValid()) {
-            $classes = $attributes->get('class');
+            $classes = $attributes->get('class')->getValue();
             if (
                 empty($classes)
                 || (is_array($classes) && ! in_array('errors', $classes))
diff --git a/src/FormElement/FileElement.php b/src/FormElement/FileElement.php
index 854d7d05..12f4217d 100644
--- a/src/FormElement/FileElement.php
+++ b/src/FormElement/FileElement.php
@@ -12,7 +12,6 @@
 use ipl\I18n\Translation;
 use ipl\Validator\FileValidator;
 use ipl\Validator\ValidatorChain;
-use ipl\Web\Widget\Icon;
 use Psr\Http\Message\UploadedFileInterface;
 use ipl\Html\Common\MultipleAttribute;
 
@@ -94,7 +93,7 @@ public function getValueAttribute()
 
     public function getNameAttribute()
     {
-        $name = parent::getNameAttribute();
+        $name = $this->getName();
 
         return $this->isMultiple() ? ($name . '[]') : $name;
     }
@@ -197,10 +196,10 @@ protected function loadFiles(): array
             } else {
                 $this->files[$name] = new UploadedFile(
                     $filePath,
-                    filesize($filePath),
+                    filesize($filePath) ?: null,
                     0,
                     $name,
-                    mime_content_type($filePath)
+                    mime_content_type($filePath) ?: null
                 );
             }
         }
@@ -374,7 +373,7 @@ protected function assemble()
         $doc = new HtmlDocument();
         if ($this->hasFiles()) {
             foreach ($this->files as $file) {
-                $doc->addHtml(new HiddenElement('chosen_file_' . $this->getNameAttribute(), [
+                $doc->addHtml(new HiddenElement('chosen_file_' . $this->getValueOfNameAttribute(), [
                     'value' => $file->getClientFilename()
                 ]));
             }
@@ -394,7 +393,7 @@ public function renderUnwrapped()
             $uploadedFiles->addHtml(new HtmlElement(
                 'li',
                 null,
-                (new ButtonElement('remove_file_' . $this->getNameAttribute(), Attributes::create([
+                (new ButtonElement('remove_file_' . $this->getValueOfNameAttribute(), Attributes::create([
                     'type' => 'submit',
                     'formnovalidate' => true,
                     'class' => 'remove-uploaded-file',
@@ -403,7 +402,7 @@ public function renderUnwrapped()
                 ])))->addHtml(new HtmlElement(
                     'span',
                     null,
-                    new Icon('remove'),
+                    new HtmlElement('i', Attributes::create(['class' => ['icon', 'fa', 'fa-xmark']])),
                     Text::create($file->getClientFilename())
                 ))
             ));
diff --git a/src/FormElement/FormElements.php b/src/FormElement/FormElements.php
index fa415a9b..6d363fd6 100644
--- a/src/FormElement/FormElements.php
+++ b/src/FormElement/FormElements.php
@@ -363,7 +363,7 @@ public function clearPopulatedValue($name)
     /**
      * Add all elements from the given element collection
      *
-     * @param Form|SubFormElement $form
+     * @param Form $form
      *
      * @return $this
      */
@@ -495,7 +495,7 @@ public function remove(ValidHtml $elementOrHtml)
             }
         }
 
-        parent::remove($elementOrHtml);
+        return parent::remove($elementOrHtml);
     }
 
     /**
diff --git a/src/FormElement/LocalDateTimeElement.php b/src/FormElement/LocalDateTimeElement.php
index 839da886..a628b57b 100644
--- a/src/FormElement/LocalDateTimeElement.php
+++ b/src/FormElement/LocalDateTimeElement.php
@@ -25,7 +25,7 @@ public function setValue($value)
             // In Chrome, if the seconds are set to 00, DateTime::createFromFormat() returns false.
             // Create DateTime without seconds in format
             if ($value === false) {
-                $format = substr(static::FORMAT, 0, strrpos(static::FORMAT, ':'));
+                $format = substr(static::FORMAT, 0, strrpos(static::FORMAT, ':') ?: null);
                 $value = DateTime::createFromFormat($format, $originalVal);
             }
 
diff --git a/src/HtmlDocument.php b/src/HtmlDocument.php
index eb471e47..e4e977e7 100644
--- a/src/HtmlDocument.php
+++ b/src/HtmlDocument.php
@@ -173,7 +173,7 @@ public function insertAfter(ValidHtml $newNode, ValidHtml $existingNode): self
             throw new InvalidArgumentException('The content does not contain the $existingNode');
         }
 
-        array_splice($this->content, $index + 1, 0, [$newNode]);
+        array_splice($this->content, (int) $index + 1, 0, [$newNode]);
 
         $this->reIndexContent();
 
@@ -195,7 +195,7 @@ public function insertBefore(ValidHtml $newNode, ValidHtml $existingNode): self
             throw new InvalidArgumentException('The content does not contain the $existingNode');
         }
 
-        array_splice($this->content, $index, 0, [$newNode]);
+        array_splice($this->content, (int) $index, 0, [$newNode]);
 
         $this->reIndexContent();
 
diff --git a/src/TemplateString.php b/src/TemplateString.php
index 611ea121..b1e01c0f 100644
--- a/src/TemplateString.php
+++ b/src/TemplateString.php
@@ -49,7 +49,7 @@ public function __construct($format, $args = null)
     /**
      * Parse template strings
      *
-     * @param null $for template name
+     * @param  ?string $for template name
      * @return HtmlDocument
      * @throws Exception in case of missing template argument or unbounded open or close templates
      */