Event Handlers
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# Case Folding

The element handler functions may get their element names case-folded. Case-folding is defined as "a process applied to a sequence of characters, in which those identified as non-uppercase are replaced by their uppercase equivalents". In other words, when it comes to XML, case-folding simply means uppercasing.

By default, all the element names that are passed to the handler functions are case-folded. This behaviour can be queried and controlled per XML parser with the xml_parser_get_option() and xml_parser_set_option() functions, respectively.

Event Handlers
Error Codes
XML Parser
PHP Manual