See my edit below. Do not use this method.
To do this purely in XPath (e.g. in a data grid), you can use:
[Date >= '[%BeginOfCurrentMonthUTC%] - [%MonthLength%]'] [Date <= '[%EndOfCurrentMonthUTC%] - [%MonthLength%]']
Updated my test case
I set my system time to 06-06-2018 (a month which has 30 days). This results in the following:
From this test case, it's clear that Stefan is correct and that this XPath should not be used. It's strange that this token can be used though: the result is unintuitive and it's missing from the documentation.
Depends a bit on your specific situation but you could do the following:
1. Create a Variable Date Time with the begin of this month minus 1, like this : addMonths([%BeginOfCurrentMonth%], -1)
2. Do the database retrieve with Xpath and compare the months with the month from date time function:
[month-from-dateTime($MonthVariable) = month-from-dateTime(createdDate)]