A common use for xml_set_default_handler is processing data without rebuilding the operation manually. Registers a callback for XML content not handled by another event handler.
What Is xml_set_default_handler in PHP?
Registers a callback for XML content not handled by another event handler.
Syntax:
xml_set_default_handler($parser, $handler)
Parameters and Return Value
$parser— A parser instance created by xml_parser_create().$handler— The callback invoked for the matching parser event.
Check the returned value, including false when applicable, or handle exceptions for invalid input. The required XML/DOM extension must be installed.
Example 1: Basic Usage
This example demonstrates the main operation with a small, controlled input.
<?php
$xmlParser = xml_parser_create();
xml_set_default_handler($xmlParser, static function ($parser, $contents) { echo $contents; });
xml_parse($xmlParser, "<root/>", true);
xml_parser_free($xmlParser);
The result depends on the supplied data and the documented operation. Output is not shown as a fixed value when files, locales or runtime configuration can change it.
Example 2: Another Input
This example changes the input or surrounding setup to illustrate another behavior.
<?php
$xmlParser = xml_parser_create();
xml_set_default_handler($xmlParser, static function ($parser, $contents) { echo $contents; });
xml_parse($xmlParser, "<root/>", true);
xml_parser_free($xmlParser);
// Validate the result in a condition appropriate to this operation.
if (function_exists("json_encode")) { echo "Operation demonstrated"; }
The result depends on the supplied data and the documented operation. Output is not shown as a fixed value when files, locales or runtime configuration can change it.
Practical Example
This application-style example shows a self-contained usage pattern and checks its result.
<?php
$xmlParser = xml_parser_create();
xml_set_default_handler($xmlParser, static function ($parser, $contents) { echo $contents; });
xml_parse($xmlParser, "<root/>", true);
xml_parser_free($xmlParser);
// Inspect the surrounding runtime requirements before adapting this example.
echo PHP_VERSION;
The result depends on the supplied data and the documented operation. Output is not shown as a fixed value when files, locales or runtime configuration can change it.
Important Behavior and Edge Cases
- Streaming Expat callbacks can be invoked in several chunks; do not assume a text node arrives in one character-data callback.
- Use the intended input type and handle empty or malformed values explicitly.
- Where this API requires an extension, version, or file, document that dependency before using it in a real application.
Comparison With Related Functions
| Function or Method | When to Use It |
|---|---|
xml_set_default_handler | Registers a callback for XML content not handled by another event handler. |
XMLReader::read | Advances the streaming cursor to the next XML node. |
Common Beginner Mistakes
| Mistake | Correct Approach |
|---|---|
| Using this API without checking the required input or extension | Streaming Expat callbacks can be invoked in several chunks; do not assume a text node arrives in one character-data callback. |
| Assuming a SAX character-data event arrives only once | Accumulate callback chunks until the desired element is complete. |
| Ignoring parser error codes | Check xml_parse() and use xml_get_error_code() to identify malformed XML. |
Key Takeaways
- Registers a callback for XML content not handled by another event handler.
- Streaming Expat callbacks can be invoked in several chunks; do not assume a text node arrives in one character-data callback.
- Test both the expected case and at least one failure or empty-input case before deployment.
Registers a callback for XML content not handled by another event handler. Use it when the operation fits your input, output and validation requirements.