XML tag naming

Every website I find gives these rules for naming XML elements:
[LIST]
[]Names can contain letters, numbers, and other characters
[
]Names must not start with a number or punctuation character
[]Names must not start with the letters xml (or XML, or Xml, etc)
[
]Names cannot contain spaces
[/LIST][FONT=inherit]However, no where in that list does it say you cannot use forward or back slashes, which cause errors. I have seen sites say to avoid periods, hyphens, etc. as some software doesn’t parse them correctly. I’ve never had a problem with periods, but have with hyphens, so I am wondering, for php (specifically using the SimpleXMLElement class) is there a list of characters to be avoided (for instance would an asterick work)?[/FONT]