Steph's pointed to this interesting set of documents. I'm going to dip into them over the next few weeks, but particularly enjoyed hearing how they're structured:
"I have found that, having started this set of notes in 1990 in the (for me) novel medium of hypertext, it has been difficult to tear free of it: my attempts to lend hierachical or serial order have been doomed to failure. Further, as ideas and these web pages have evolved, it has been important for me to be able to reorganize my thoughts, grab a new leaf, shake the tree and regard it as the root. So the reader needs to be aware of this, that each page may be an attempt to put across a given concept serially, but if you are looking for an order of concepts and subconcepts, you have as much hope as you would with words in the dictionary. "