Name
Processing Instructions
Synopsis
<?
target
processing-instruction data
?>
Processing instructions provide an escape mechanism that
allows an XML application to include instructions to an XML
processor that are not validated. The processing instruction
target can be any legal XML name, except xml
in any combination of upper- and
lowercase (see Chapter 2).
Linking to a stylesheet to provide formatting instructions for a
document is a common use of this mechanism. According to the
principles of XML, formatting instructions should remain
separate from the actual content of a document, but some
mechanism must associate the two. Processing instructions are
significant only to applications that recognize them.
The notation facility can indicate exactly what type of processing instruction is included, and each individual XML application must decide what to do with the additional data. No action is required by an XML parser when it recognizes that a particular processing instruction matches a declared notation. When this facility is used, applications that do not recognize the public or system identifiers of a given processing instruction target should realize that they could not properly interpret its data portion.
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