I've been getting this error message as I build up HTML code, and I finally realized that what was wrong was a missing comma, for instance after the.header(…) here. It might be good to document the error message phrase _"Cannot infer contextual base in reference to member _____" for people who encounter this error in the future.

(This is using Xcode 12 beta; don't know how it will appear in older or newer versions of the Swift compiler…)