```ruby
AbortError = Class.new(StandardError)
```

This is a minor detail, but in idiomatic Ruby user-defined exception classes generally extend `StandardError`. Direct descendants of `Exception` are generally reserved for the interpreter. An unqualified `rescue` block (line 118) catches `StandardError` so extending `Exception` directly is often considered bad form.

The `Class.new` syntax is shorthand for defining a subclass without additional implementation so it collapses lines 86-7 into one line.