Varieties in the Field

XML has developed more variety than perhaps it should

Myth XML is XML is XML, which can be shared easily across many different applications and platforms. According to this popular story, any XML processor should be able to read any XML document and at least get the content and structure even if it doesn't understand the 'meaning.'
Reality Different parsers have supported different subsets of XML functionality. The initial validating/non-validating distinction has become validating/non-validating with defaulting/non-validating without defaulting and varying levels of namespace support complicate the picture even more drastically.