Remove mentions of empty strings for React 18

[karlhorky]

Ref: #3203 (comment)

Also cleans up some formatting in the JSX examples

[codecov]

Codecov Report

Merging #3468 (dfd64ae) into master (c02d4e3) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3468   +/-   ##
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  Coverage   97.57%   97.57%           
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  Files         129      129           
  Lines        9212     9212           
  Branches     3342     3342           
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  Hits         8989     8989           
  Misses        223      223           

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[karlhorky]

@ljharb what do you think about this one? Or is this approach with this first docs PR not what you had in mind?

[ljharb]

With the merging of #3488, the behavior is now corrected for the React version as well.

[karlhorky]

Great, thanks!