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There are new strings present in the default locale properties file for forms/flows in v5. For example.: strings for mobile devices. You will need to manually add these new strings to your uploaded locale files for forms created in v4. New strings can be found by downloading the v5 default properties file for your form. Server wide customizations can be done by unzipping the <frevvo-home>/tomcat/webapps/frevvo.war. See this documentation for the details.

Data API

The browser doc feature in  v4 is no longer supported. It introduced a new doc action that can be enabled by the API and where, on submission, the XML document would be sent back to the browser with the HTTP response. This enabled the capture of updated XML and make sure it updated their own systems in a single db transaction.

 In 5.x, we have a new mechanism. It is possible now to submit forms using the API and receive back a DataSource? with multiple parts (multipart/form-data) one for each submission document: XML, snapshot, attachments, etc. This is above and beyond what the browser docs provide, but much simpler. See API's submitInstance() and Data Source documentation (coming soon...). 

Dates & Time Initialization in a form.load Rule

Rules initializing dates & time Time and Date/Time controls will not work in a form.load rule unless you specify a timezone on the form's Url via the _formTz Url parameter. This is because the form server needs to know the timezone in which to return the date and time. If you do not specify a _formTz the methods will return null and the control values will remain blank. Timezone strings you can use in the parameter can be found here. For example, to specify Eastern time append &_formTz=America/NewYork to the form Url.  This parameter is not needed if your form/flow only contains date controls.