What's the meaning of the underscore in the java api's methods, e.g., _toQuery()

_toQuery() is a public method that's used in examples on public docs (like Searching for documents | Elasticsearch Java API Client [8.13] | Elastic), so the method isn't internal - something the underscore sometimes represents.

So what is the significance of methods that start with underscore in the java api?

Just curious and kinda wondering if I should be avoiding them.