Don't operate on a collection and a range of indices if you can help it.

[dabrahams]

I just noticed https://developer.apple.com/documentation/swift/customconsumingregexcomponent/consuming(_:startingat:in:)

In general APIs are cleaner if you just operate on collections and use slices to limit what you're looking at. Obviously if that's not possible in this case, please ignore. Otherwise, please apply as broadly as possible ;-)

[porglezomp]

Components may need to access outside the matched range to determine if they match. Consider for example a word boundary: it has to look at both the previous and current character to check if it matches at the current position, so a slice of the collection is not appropriate since you can't access it out-of-bounds.