TLDR: the gist of it is that one of Apple's XML parsers treat XML comments wrong and would advance a char pointer only two bytes when it should advance three by

TLDR: the gist of it is that one of Apple's XML parsers treat XML comments wrong and would advance a char pointer only two bytes when it should advance three bytes (eg. past "!--") such that this invalid XML comment passes <!---> whereas another parser correctly rejects the invalid XML comment. I don't see how this is a reason to hate on XML. A similar bug can surface in any property file parsing routine for a format having commenting syntax. It's amplified, though, by Apple (according to TFA) using four different XML parser implementations for parsing entitlement and other property (.plist) files, and the lack of testing/dilution of efforts that goes with a situation like this. I'll add that .plist files (or other simplistic property files for that matter) IMO had never a good reason to be XML. XML/SGML is really for delivery/authoring rich semi-structured text in a plain text editor (and is second-to-none for this use case). To me it seems that in this case using XML in the first place because it's already a widely (mis-)used format for general-purpose data serialization, and then not actually using an industrial-strength XML parser (such as libxml2, expat, or xerces) but coding your own ad-hoc XML parser instead is particular bad practice.