ProcessingInstruction

« Gecko DOM Reference

A processing instruction provides an opportunity for application-specific instructions to be embedded within XML and which can be ignored by XML processors which do not support processing their instructions (outside of their having a place in the DOM).

A Processing instruction is distinct from a XML Declaration which is used for other information about the document such as encoding and which appear (if it does) as the first item in the document.

User-defined processing instructions cannot begin with 'xml', as these are reserved (e.g., as used in <?xml-stylesheet ?>).