__ATTRIBUTES__(UNKNOWNISERROR) has been removed. You can use STATIC OBJECTTYPE (which mostly has the same effect) or
simply remove the attribute.
GetCloneableEntityFields also removes the WRD_TAG from the clone, which makes more sense given its task (preparing for a new CreateEntity)
Support for ?whs-download and ?whs-download= URLs has been removed. You'll need to use <a download> links from now on.
'allowwitty' and 'nowebdesign' fields for HTML files have been removed.
moduledefinition <dependency> no longer accepts requirerevision=
The WebForm API has been removed from the WebBrowser object (->OpenForm). You can just use DOM manipluation and ->SubmitForm
Things you should do
Things that are nice to know
New command line module dev tools: wh module create and wh module createwebdesign, replacing ?app=system:devools
Error pages now add wh-errorpage and wh-errorpage-NNN (with NNN being 404, 500, etc) classes to the <html> element
Introducing a new option source <fslibrary fslibrary="mylibrary" />, which can be used in selects to show the contents of a
library defined by <setlibrary name="mylibrary">.
A <setlibrary>'s <source> can now have a path relative to the target object itself, instead of only relative to the
target object's parent site. I.e. you can now specify <source path="mydir" relativeto="targetobject" /> to point to the
target object's mydir subdirectory if the target object is a folder, or to the directory mydir in the target object's
parent folder if the target object is a file.
Added 'QS' and 'QSA' members to the WebBrowser as a shorthand for document->QuerySelector(All).
Form input elements can set the attribute data-wh-form-skipnativevalidation to skip the HTML5 native validity checks
allowing you to use your own validations and error messages.
Various XML attributes which used __MatchesAnyMask switched to MatchCommonXMLWildcardMasks, which allows excluding
certain masks (eg applicationmasks="* !mymodule:* mymodule:exceptmyapp")
7500 OO 296 can be entered into an address field to check with verification provider is configured
Siteprofile <wrd:addressvalidation> can now refer to a wrdschema (but registry keys still take precedence)
moduledefinition <dependency> can now declare a requireversion= which will be semver-matched against the remote server.
If you use this version, be sure to also set at least requireversion="42002" on <packaging> (WebHares prior to 4.20.02
do not accept 'requireversion' in module definitions).