Moreover, there is a clear arc to Alexander's career that goes a little like:
• Mathematical era (PhD/Notes on the Synthesis of Form, A City is not a Tree)
• Pattern era (Timeless Way, APL, and about four case studies)
• 15 properties era (Nature of Order)
As one might expect, a lot of the earlier work is recapitulated in the later work, but the fact that he explicitly deprecated patterns at his OOPSLA 1996 keynote (https://youtu.be/98LdFA-_zfA ) is important. People are aware of APL because of Gang of Four and Richard Gabriel etc but not so much that lecture.
As for the fifteen properties in Nature of Order, they mainly concern Euclidean geometry and the ordinary physics one would associate with constructing actual buildings. The evidence that they would need to be adapted to a more generic semiotic-topological domain such as software is the fact that Alexander himself saw fit to draw up (in Book 4) eleven analogous properties pertaining exclusively to colour (a 1:1 correspondence except for four which coalesce two of the geometric properties each). Concepts like "life", "wholeness", "center", "the fundamental differentiating process" etc. can be used unchanged.