Been following the timeline, I've often wondered "when or which version will the change made to in Chrome or Safari?"
Although there are feature flags so not all changes are applied, but it is still helpful to show the corresponding WK version number, which can be obtained from /WebCore/Configurations/Version.xcconfig.
add wkversion.js to show wk version number. closes #2.
first cut. it is inefficient given each time the page shows it sends a request to Version.xcconfig, which updates less often. gotta do something so that it first memorize the latest version...