This shows which characters are allowed as a tag name with the document.createElement API.
try{0x0D
document.createElement(String.fromCodePoint($[i]));0x0D
log($[i])0x0D
} catch{}try{0x0D
document.createElement(String.fromCodePoint(58));0x0D
alert(58)0x0D
} catch{}try{0x0D
document.createElement(String.fromCodePoint(95));0x0D
alert(95)0x0D
} catch{}