Converts a node to a string but only serializes the node's contents.
* `node`: A node within the document to serialize, defaults to the document itself.
* `config`: A configuration array with the possible keys and value types being:
- `booleanAttributeValues` (`bool|null`): Whether to include the values of boolean attributes on HTML elements during serialization. Per the standard this is `true` by default
- `foreignVoidEndTags` (`bool|null`): Whether to print the end tags of foreign void elements rather than self-closing their start tags. Per the standard this is `true` by default
- `groupElements` (`bool|null`): Group like "block" elements and insert extra newlines between groups
- `indentStep` (`int|null`): The number of spaces or tabs (depending on setting of indentStep) to indent at each step. This is `1` by default and has no effect unless `reformatWhitespace` is `true`
- `indentWithSpaces` (`bool|null`): Whether to use spaces or tabs to indent. This is `true` by default and has no effect unless `reformatWhitespace` is `true`
- `reformatWhitespace` (`bool|null`): Whether to reformat whitespace (pretty-print) or not. This is `false` by default
##### Examples #####
- Serializing a document (functionally identical to `Document::serialize`):
```php
namespace MensBeam\HTML\DOM;
$d = new Document('<!DOCTYPE html><html></html>');
echo $d->serializeInner();
```
or:
```php
namespace MensBeam\HTML\DOM;
$d = new Document('<!DOCTYPE html><html></html>');
Common namespace constants are provided in `MensBeam\HTML\DOM\Node` to make using namespaces with this library not so onerous. In addition, constants are provided here to be used with `MensBeam\HTML\DOM\ParentNode::walk`. `MensBeam\HTML\DOM\Node` also implements `\Stringable` which means that any node can be simply converted to a string to serialize it.
Common namespace constants are provided in `MensBeam\HTML\DOM\Node` to make using namespaces with this library not so onerous. In addition, constants are provided here to be used with `MensBeam\HTML\DOM\ParentNode::walk`. `MensBeam\HTML\DOM\Node` also implements `\Stringable` which means that any node can be simply converted to a string to serialize it.