My personal (today) opinion is that the Gothic Romance is over romantisized.
Those "flying buttresses" were added decades or centuries later because the cathedral was going to fall down,
but later were viewed as part of the art ...
Plus comparing architecture to markup I think is a catwalk.
Architecture has to follow natures laws ... those are implicit ... The building has to hold up to gravity and decay and use.
Those things are a given. But to compare to XML with schema ... I would argue that Schema is the natural law.
It imposes those things which have to be upheld ( the building still stands under gravity, it can hold a congregation of X,
it has a ceiling hight of Y , the walls dont fall down, it costs less then $X) It keeps the tempature above YdegC .. It doesnt stink of mold.
To claim an equivalence to gothic architecture and schema-less XML to me seems nonsensical.
Surely there is a range of constraints .... but to claim gothic architecture had no constraints is just plain silly.
If it had no constraints it would be a Escher painting, not a building.