I&#x27;m almost positive we have worked together (your handle stuck out... percussion?)... I agree the extension&#x2F;validation parts of XML are not well understood (DTD, entity references, namespaces) but in general rarely used or needed.<p>Most uses of XML in the past and today use just mainly tags and attributes. XML purpose was for an extensible document format <i>not</i> a general purpose programming language, DSL and&#x2F;or a serialization format. For its original <i>purpose</i> it isn&#x27;t a terrible format.<p>Document formats require special handling of space and comments and repeated nodes (see my other comments). Even S-Expressions ignore spaces in general so are probably not a good format for documents.