I've done my fair share of systems integrations and the number of teams that did not know xml or have never used it in a professional settings was around 20%. Of those who did use it a staggering amount of people never understood namespaces and started testing for equality on the element name and namespace prefix string instead of the namespace declaration. When somebody claims they "know" xml I initially treat it as a developer saying that he/she knows 'sql' while reviewing their code and seeing them do joins in the application logic.