The "Summary" of op:dateTime-equal states:

<quote>
Returns true if and only if the value of $arg1 is equal to the value of $arg2 according to the algorithm defined in section 3.2.7.4 of [XML Schema Part 2: Datatypes Second Edition] "Order relation on dateTime" for xs:dateTime values with timezones.
</quote>

There is no mention here, or anywhere else except the examples, of the role of the implicit timezone. The information in the summary seems at best misleading and at worst plain incorrect: the only way it can be made consistent with the examples is by assuming that the implicit timezone is treated implicitly as part of the values used as input to the algorithm from the XML Schema specification.

The same problem applies to all the other comparison functions for dates/times.

The introductory paragraphs to section 10.4 describe the general approach to comparing dates and times by filling in missing components from the 7-field model; but the specific functions do not refer to that material directly (instead it refers directly to the schema specification). Indeed the introductory material only says that the implicit timezone is used "in some cases", but it does not say which.