Impressed with Appender - Is there design/implementation description?

[Jon Degenhardt via Digitalmars-d-learn]

I've been using Appender quite a bit recently, typically when I 
need append-only arrays with variable and unknown final sizes. I 
had been prepared to write a custom data structure when I started 
using it with large amounts of data, but very nicely this has not 
surfaced as a need. Appender has held up quite well.

I haven't actually benchmarked it against competing data 
structures, nor have I studied the implementation. I'd be very 
interested in understanding the design and how it compares to 
other data structures. Are there any write-ups or articles 
describing it?

--Jon