What scares me is that this is actually a much lower compatibility expectation than Posix ever achieved. It is possible to use strict Posix APIs, whether "larg

What scares me is that this is actually a much lower compatibility expectation than Posix ever achieved. It is possible to use strict Posix APIs, whether "large and widely touted" or not, and always has been. It is not and never has been possible to treat Posix as a single interoperable platform, because every Unix vendor wound up developing their own APIs much faster than the Posix process could standardize this. Also, once vendor APIs diverge in semantics, whether because of implementation errors or spec ambiguities/inconsistencies, these differences become permanent, as no vendor wants to break the existing code of a developer who was loyal enough to target their platform in the first place. And everyone has a motivation to "extend and embrace," of course. Can anyone name some factors that mitigate these effects in the HTML5 context?