The "SGML WG", which eventually became the "XML Special Interest Group", came into existence on August 28, 1996. In practice, the smaller group (WG) marshaled issues for debate, then the larger group (SIG) debated, then the WG resolved things by voting. In practice, this often failed to settle important issues; on several, the SIG simply refused to accept the results of the vote and bullied the WG until it reversed itself.
The important thing about the SIG is the breadth of its membership (including, crucially, SGML luminaries such as Charles Goldfarb, Dave Peterson, and James Mason), and the quite frankly astounding amount of time they were able to put into the process.
The important thing about the WG is how well the process worked. Its discussions and votes, which are a matter of public record, reveal that while the WG often failed to achieve unanimity, it did achieve consensus in the important meaning of the word, as evidenced by the fact that members of the WG are often willing to defend aspects of XML which they personally voted against.
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