I have a book with some (decorative parts) plus an introductory chapter with things like notation conventions. It is distinct from the preface.
My preference would be to put this chapter in the front matter, but this creates a numbering discrepancy: with the default of numbering starting at 1, this shows up as Chapter 1 in the HTML and Chapter 0 in the LaTeX. If I change the numbering to start at 0, this shows up as Chapter 0 in the HTML and Chapter -1 in the LaTeX, so in both cases it is the LaTeX version that is not numbering according to specifications.
There are other ways to deploy this chapter (e.g., in its own Part 0, or as a separate chapter not included in a part). But putting it in the front matter should either work correctly (with consistent numbering) or be deprecated/disallowed.
Best,
Kiran