The title of this category reminded me that a couple of years ago I collected pretty much all the AppleScript developer documentation I could find while PDFs were still available, and dumped them into a website* here:
*as the website is a freebie wordpress.com blog, you may be subjected to Wordpress’s ads unless you have an adblocker installed. Please note the ads are nothing to do with me, nor do I receive revenue from them.
Wow ! You’re the one behind that site! Amazing! I always wondered who it was who did this 
While I’m at it, here’s a link to Apple’s Sketch sample code, which although it contains loads of deprecations and hasn’t been updated (possible BR?) since 2012, still runs if you set the Deployment Target to whatever your machine is on.
Sketch gives a good example of an sdef and how to link it to your classes (it appears I’ve been doing it wrong, subclassing NSScriptCommand for each of my scripting commands, which works, but appears to be redundant).
https://developer.apple.com/library/content/samplecode/Sketch/Introduction/Intro.html