I managed to work this out. x/x and x/? fics get just the first number; x/y fics get both.
Please let me know if any improvements to be made:
Code:
[defaults]
# 'add_to_' concats on to existing param, thus the leading comma
add_to_extra_valid_entries:,oneshot,tagscategory,covertype,ao3chaps
[archiveofourown.org]
## Chapter formatting
include_in_ao3chaps:chapterslashtotal
ao3chaps_label:Chapters
titlepage_entries: seriesHTML,category,genre,language,characters,ships,status,datePublished,dateUpdated,dateCreated,rating,warnings,ao3chaps,numWords,publisher,description
add_to_replace_metadata:
ao3chaps=>^(\d+)/\1$=>\g<1>
ao3chaps=>^(\d+)/\?$=>\g<1>