Regex doesn't seem to work as describe in that article.
The advice is to avoid regex if possible due to it being expensive, however I'd still like to understand it.
From the article:
For example if we search for
author:/[Dd]ouglas.*[Aa]dams/in the unanalyzed data, it will yield the two documents, since there was an entry for "Douglas Adams" in the inverted index.
So these should work but they all return zero hits:
useragent.name:/Chrome/
useragent.name:/[Cc]hrome/
useragent.name:/[Cc]hrome.*/
These do work:
useragent.name:/.hrome/
useragent.name:/.hrome.*/