GET /articles?include=author&fields[articles]=title,body,author&fields[people]=name HTTP/1.1
Because you want to include the “author” relationship in each article. (“people” is a type name, rather than a relationship/field name.)
Breaking the request into parts:
GET /articles?include=author: Give me the articles and, for each article, include it’s author resource
&fields[articles]=title,body,author: (But) for resources of the the articles type, include only the title, body, and author fields.
&fields[people]=name: (And) for resources of the people type (which are present in included, but could theoretically have been part of the primary data too, if you’d asked for a different collection), include only the name field.
would GET /articles?include=author&fields[articles]=title,body,author&fields[author]=name
work out better since you could have more relationships (for example: editor) with type people in them? I could want a different set of fields for those relationships.
It seems redundant that you would include an author and must have them listed in the fields section.
Why would I include them if I wasn’t going to use their info?