PHP xml_set_notation_decl_handler() Function

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The PHP XML Parser xml_set_notation_decl_handler() function is used to set a function to be called when the parser finds a notation declaration in the XML document. The handler parameter can also be an array containing an object reference and the method name.

So basically in an XML document, this function allows you to define a callback, or specific function, to handle notation declarations.

The system or structure for handling particular data is defined using notations in XML. This function is useful when handling or processing such declarations during XML parsing.

Example use cases −

• For examining or manipulating complex XML files.

• When working with specific external data type XML instructions.

Syntax

Below is the syntax of the PHP XML Parser xml_set_notation_decl_handler() function −

true xml_set_notation_decl_handler ( XMLParser $xml_parser, callable|string|null $handler )

Parameters

Here are the parameters of the xml_set_notation_decl_handler() function −

• $xml_parser: (Required) It is a reference to the XML parser to the XML parser to set up notation declaration handler function.

• $handler: (Required) It is used to specifies a function to be used as an event handler.

Return Value

The xml_set_notation_decl_handler() function returns TRUE on success. And FALSE on failure.

PHP Version

First introduced in core PHP 4, the xml_set_notation_decl_handler() function continues to function easily in PHP 5, PHP 7, and PHP 8.

Example 1

First we will show you the basic example of the PHP XML Parser xml_set_notation_decl_handler() function to how to use the same callback function with a simple $xml string containing a notation declaration.

<?php
   // Callback function 
   function notationHandler($p, $notationName, $base, $systemId, $publicId) {
      echo "Notation: $notationName, System ID: $systemId, Public ID: $publicId\n";
   }

   // Create an XML parser
   $p = xml_parser_create();

   // Set the notation declaration handler
   xml_set_notation_decl_handler($p, 'notationHandler');

   // Simple XML with a notation declaration
   $xml = <<<XML
   <!DOCTYPE note [
      <!NOTATION myNotation SYSTEM 'notation.dtd'>
   ]>
   <note>
      <to>Tina</to>
      <from>Suresh</from>
      <message>Hello, world!</message>
   </note>
   XML;

   // Parse the XML string
   xml_parse($p, $xml);

   // Free the parser
   xml_parser_free($p);
?>

Output

Here is the outcome of the following code −

Notation: myNotation, System ID: notation.dtd, Public ID: 

Example 2

In the below PHP code we will use the xml_set_notation_decl_handler() function and parse an XML document with multiple notation declarations and processes them.

<?php
   // Callback function 
   function notationHandler($p, $notationName, $base, $systemId, $publicId) {
      echo "Notation Found: $notationName\n";
      echo "System ID: $systemId, Public ID: $publicId\n";
   }

   // Create XML parser
   $p = xml_parser_create();

   // Assign handler
   xml_set_notation_decl_handler($p, 'notationHandler');

   // Parse an XML string 
   $xml = "<!DOCTYPE note [
      <!NOTATION jpeg SYSTEM 'image/jpeg'>
      <!NOTATION png SYSTEM 'image/png'>
   ]>";
   xml_parse($p, $xml);

   // Free the parser
   xml_parser_free($p);
?> 

Output

This will generate the below output −

Notation Found: jpeg
System ID: image/jpeg, Public ID: 
Notation Found: png
System ID: image/png, Public ID: