How to get started with svn:externals?

I'm looking for a succinct and well-written tutorial on using svn:externals.

I already know how to use them in a basic way myself, but I want a good article that I can link to when answering questions like this one that come up recently:

http://stackoverflow.com/questions/662898/what-to-do-with-multiple-projects-depend-on-the-same-source/662905

I'd do it myself, but I don't use them often enough to want to stick my neck out and write a tutorial on it. Google was surprisingly unhelpful with this topic.

From stackoverflow

• I wrote a tutorial and put it on my site, because this is a much asked question. Also, I always forget how to do this, and I need to look it up all the time.

  Shared Repositories using SVN Externals

• Here are som sections about it in the svnbook / TortoiseSVN manual:

  • http://tortoisesvn.net/docs/release/TortoiseSVN_en/tsvn-howto-common-projects.html#tsvn-howto-common-externals
  • http://tortoisesvn.net/docs/release/TortoiseSVN_en/tsvn-dug-import.html#tsvn-dug-import-4
  • http://svnbook.red-bean.com/en/1.5/svn.advanced.externals.html