While studying the text and code of the 'HOWTO write an External for puredata' found at http://iem.at/pd/externals-HOWTO/HOWTO-externals-en.html, I made some help patches, comments in the code and variations on the externals. It is probably most useful as an addition to the original text at iem.
As I thought it might be of interest to others, there are also executables (Linux, MacOSX, Windows) for those currently without a development environment.
The original page is here: http://fjkraan.home.xs4all.nl/digaud/puredata/ExternalsHowto/
(it seems I can attach only one attachement, and it is limited in size, so this contains only the basic examples.)