APA7 style bug: capitalization of several subtitles
According to APA7, the first word of a subtitle should be capitalized (https://apastyle.apa.org/style-grammar-guidelines/capitalization/title-case). The CSL style does this for the first subtitle, but not for more than one subtitle.
This is my title: With a nice subtitle: but some authors just use more: and more: and more
This is my title: With a nice subtitle: but some authors just use more: and more: and more
Alternatively you might be looking at a part or volume title, which can be added to the Extra field using the following form:
volume: 3
volume-title: Volume the third
part-number: 2
part-title: Part the second