When you created any tag name in XML keep this rules in mind.
Rule1: Tag name should be start with a letter or underscore\'_\'.
Rule2: XML does not reserve pre-defined tags.So, you can made your own tags as per requirement.
Rule3: We can also use digits(0123456789), hyphen(-),period(.) and \':\'.But don\'t use them unnecessary because these we also use when creating Namespaces.