Notations and Processing Instructions

Two features of XML that are holdovers from SGML and very rarely used are Notations and Processing Instructions. We will cover them briefly here, but they are both specialized enough that should you have the need to use either of them extensively you should consult either the XML 1.0 Recommendation or a text that deals exclusively with advanced XML development. Chances are you'll never use notation or processing instructions; but if you do that, you are coming from an SGML background and are already familiar with their use.