Currently @preserveOrder on <sequence> is an optional attribute and the spec states: "if true, indicates that the order in which component elements of a sequence appear in a document must correspond to the order in which they are given in the content model." However, the default behaviour for <sequence> is that order is preserved unless @preserveOrder is false, but the current description makes it seem that the opposite is true (i.e. that order doesn't matter by default); plus, ​setting to false hasn't worked since at least 2017 per TEIC/Stylesheets#241.

Since @preserveOrder is implicitly true, I think that it should gain a default value of true so that it states explicitly what's already happening; I would also suggest that the description be changed to reflect that "true" is default and also outline what happens when its value is "false".