DOMDocument

DOMDocument is a class in PHP’s DOM extension that represents an entire XML or HTML document and provides a programmatic interface to traverse and modify the document tree according to the W3C DOM API. It is built on top of the libxml2 library and exposes standard DOM methods for common document operations, including support for namespaces and mixed content.

A new instance is created with optional version and encoding, for example: new DOMDocument('1.0', 'UTF-8'). It can parse content from strings or files using loadXML, load, loadHTML, and loadHTMLFile. Once loaded, the document tree can be navigated via properties such as documentElement, and nodes can be created and inserted using createElement, createTextNode, and appendChild. The API mirrors the W3C DOM Core, with added conveniences for PHP such as createElementNS for namespace-aware elements and DOMXPath for XPath queries.

For output, DOMDocument provides serialization methods such as save, saveXML, and saveHTML, which write to a file or return the serialized markup when no filename is supplied. Output can be formatted with formatOutput, and whitespace handling can be controlled with preserveWhiteSpace.

Validation and error handling are supported through libxml features. The document can be validated against a DTD or XML Schema via schemaValidate and relaxNGValidate, and libxml error handling can be configured with libxml_use_internal_errors.

Common use cases include processing XML data, generating or transforming XML feeds, and manipulating HTML content. DOMDocument is part of PHP’s standard DOM extension and interoperates with DOMXPath for complex queries, making it a versatile tool for XML and HTML work in PHP projects.