The way I see it, this question follows The Six Subjective Question Guidelines:
- It inspires answers that explain "why". Options are given, so I need reasons.
- Long answers are expected which provide example implementations and reasons for designing them that way (like why
XDocumentdoes not follow specification).
- It's not a holy war topic, so constructive tone is expected.
- It invites sharing experiences, because there're many standards implemented both by Microsoft and third-parties.
- As per above, facts and references are expected.
- And finally, it's a very important practical question about designing libraries.
The way I see it, the question perfectly fits Programmers scope: conceptual questions about software development. It is about software architecture which is declared as on-topic by FAQ.
So, the question is: why was the question closed and how to fix it to get it reopened?