This article talks about TypeScript Transformers. A Transformer allows to execute pre and post compilation processing with our TypeScript sources which can be helpfull when you're adding a file extension to an import declaration for example.
The Span<T> is a value type added since C# 7.2. This was released in November 2017, so it should be a known feature by now... However not a lot of people actually know what it does, why it was added or how you use it. Let's have a look.