At first I was afraid that my book was to be sheer plagiarism. But I was encouraged by the discovery that if you steal your ideas from one author, that is plagiarism; whereas if you lift them from many, that is research.
If he were alive today, Davidson would undoubtedly be a keen blogger.
Murray described the King's Leap in separate sections in his chapter on 'The Mediaeval Game'. One section addressed chess in Spain, another addressed chess in Italy. Here's what he had to say about the Spanish game (p.457-461).
In fact, except for point (4) in the second part, most of the material I've excerpted has nothing to do with the King's Leap. I've left in the rest to establish the period covered, to show Murray's own sources (MS. Alf. is the Alfonso manuscript and is well described on other Web pages), and to overview the rules of the pre-modern game at that time, particularly the Queen, the Bishop, and the Queen's leap.