Enhancement: bookpart-local page numbering
This feature has been requested quite a few times on -user and -user-fr:
A paper variable to number pages per bookpart instead of sequentially for the whole book. This can be useful if you are publishing a set of instrumental parts that are joint in a single book, perhaps with a common introduction, but intended to be used separately. Furthermore, setting this variable only for the first bookpart in conjunction with
page-number-type could be used to number pages in the introductory material with separate numbering and in roman numbers, which is common practice.