Are there differences between XML and HTML special character encoding?

Question

Are there any characters that are encoded in HTML but not XML, or vice versa?

Are all the encodings the same between them? Like > for greater than symbol?

Answer 1

XML does predefine a handful of character entities. See section 4.6 of the XML 1.1 spec:

http://www.w3.org/TR/xml11/#sec-predefined-ent

In particular, XML defines <, >, &, ', and " ("All XML processors MUST recognize these entities whether they are declared or not").
Any other entities must be referenced via numeric reference, as Brian states, or by an appropriate definition in an <!ENTITY ...> construct in the document itself or a referenced DTD.

All of these entities are defined in HTML as well.