Is a colon a legal first character in an XML tag name?

Question

According to the W3C XML Recommendation, start tag-names have the definition:

STag ::= \'<\' Name (S Attribute)* S? \'>\'

..where

Answer 1

They are allowed in non-namespace-aware XML but they are not allowed in namespace-aware XML. More specifically, the base XML recommendation allows them but the Namespaces recommendation prohibits them. Very few people nowadays use non-namespace-aware XML (and I'm not sure what parsers support it) so it's best to assume they aren't allowed.