How do I add custom items to my docsearch crawler?

Refer to this doc. The "selectors" indicate what nodes in the document it uses to get the information. For example p#someId would target a paragraph with "someId" as the id. The defaultValue just is a set of values that is uses as a fallback if the selectors don't exist. 

You can run any vanilla js in the record extractor function as well, and pass things as variables to the defaultValue.